VOLUME 1


    IPCS/CEC Evaluation of Antidotes Series

    IPCS   International Programme on Chemical Safety
    CEC    Commission of the European Communities

    Volume 1   Naloxone, flumazenil and dantrolene as antidotes
    Volume 2   Antidotes for poisoning by cyanide

    This important new series will provide definitive and authoritative
    guidance on the use of antidotes to treat poisoning.  The
    International Programme on Chemical Safety (IPCS) and the Commission
    of the European Communities (CEC) (ILO/UNEP/WHO) have jointly
    undertaken a major programme to evaluate antidotes used clinically
    in the treatment of poisoning.  The aim of this programme has been
    to identify and evaluate for the first time in a scientific and
    rigorous way the efficacy and use of a wide range of antidotes.
    This series will therefore summarise and assess, on an antidote by
    antidote basis, their clinical use, mode of action and efficacy. The
    aim has been to provide an authoritative consensus statement which
    will greatly assist in the selection and administration of an
    appropriate antidote. This scientific assessment is complemented by
    detailed clinical information on routes of administration,
    contraindications, precautions and so on.  The series will therefore
    collate a wealth of useful information which will be of immense
    practical use to clinical toxicologists and all those involved in the
    treatment and management of poisoining.

    Scientific Editors

    Department of Health, London, United Kingdom

    Ulleval University Hospital, Oslo, Norway

    International Programme on Chemical Safety,
    World Health Organization, Geneva, Switzerland

    Health and Safety Directorate,
    Commission of the European Communities, Luxembourg

    EUR 14797 EN

    Published by Cambridge University Press on behalf of the World Health
    Organization and of the Commission of the European Communities


    The mention of specific companies or of certain manufacturers'
    products does not imply that they are endorsed or recommended by the
    World Health Organization in preference to others of a similar
    nature that are not mentioned.

    Neither the Commission of the European Communities nor any person
    acting on behalf of the Commission is responsible for the use which
    might be made of the information contained in this report.

    (c) World Health Organization, Geneva, 1993 and
    ECSC-EEC-EAEC, Brussels-Luxembourg, 1993

    First published 1993

    Publication No. EUR 14797 EN of the Commission of the European
    Communities, Dissemination of Scientific and Technical Knowledge
    Unit, Directorate-General Information Technologies and Industries,
    and Telecommunications, Luxembourg

    ISBN 0 521 45459 X hardback






         2.1. Introduction
         2.2. Name and chemical formula
         2.3. Physico-chemical properties
         2.4. Pharmaceutical formulation and synthesis
         2.5. Analytical methods
               2.5.1. Quality control
               2.5.2. Identification
               2.5.3. Quantification of the antidote
               2.5.4. Analysis of toxic agents
         2.6. Shelf-life
         2.7. General properties
         2.8. Animal studies
               2.8.1. Pharmacodynamics
               2.8.2. Pharmacokinetics
               2.8.3. Toxicology
         2.9. Volunteer studies
               2.9.1. Pharmacokinetics
               2.9.2. Pharmacodynamics
               2.9.3. Effects of high doses of naloxone
         2.10. Clinical studies - clinical trials
               2.10.1. Effects in therapeutic use of opioids
               2.10.2. Effects in acute opioid poisoning
         2.11. Clinical studies - case reports
               2.11.1. Naloxone in clonidine poisoning
         2.12. Summary of evaluation
               2.12.1. Indications
               2.12.2. Advised routes and dose
               2.12.3. Other consequential or supportive therapy
               2.12.4. Areas where there is insufficient information
                       to make recommendations
               2.12.5. Proposals for further studies
               2.12.6. Adverse effects
               2.12.7. Restrictions of use
         2.13. Model information sheet
               2.13.1. Uses
               2.13.2. Dosage and route
               2.13.3. Precautions/contraindications
               2.13.4. Adverse effects
               2.13.5. Use in pregnancy and lactation
               2.13.6. Storage
         2.14. References


         3.1. Introduction
         3.2. Name and chemical formula of antidote
         3.3. Physico-chemical properties
         3.4. Pharmaceutical formulation and synthesis
         3.5. Analytical methods
               3.5.1. Identification of the antidote
                Infrared spectroscopy
                Ultraviolet absorption
                Thin-layer chromatography
               3.5.2. Quantification of the antidote in biological
               3.5.3. Analysis of the toxic agent in biological
         3.6. Shelf-life
         3.7. General properties
         3.8. Animal studies
               3.8.1. Pharmacodynamics
               3.8.2. Pharmacokinetics
               3.8.3. Toxicology
                Acute toxicity
                Subacute toxicity
                Chronic toxicity
         3.9. Volunteer studies
               3.9.1. Pharmacodynamics
                BZD antagonist effect
                Intrinsic effects
               3.9.2. Pharmacokinetics
               3.9.3. Tolerance of flumazenil
               3.9.4. Other studies
         3.10. Clinical studies - clinical trials
               3.10.1. Anaesthesiology
               General anaesthesia
               Conscious sedation
               3.10.2. Benzodiazepine overdose or intoxication
         3.11. Clinical studies - case reports
         3.12. Summary of evaluation
               3.12.1. Indications
               3.12.2. Dosage and route
               3.12.3. Other consequential or supportive therapy
               3.12.4. Areas where there is insufficient information to
                       make recommendations

               3.12.5. Proposals for further study
               3.12.6. Adverse effects
               3.12.7. Restrictions of use
         3.13. Model information sheet
               3.13.1. Uses
               3.13.2. Dosage and route
               3.13.3. Precautions/contraindications
               Pharmaceutical precautions
               Other precautions
               3.13.4. Adverse effects
               3.13.5. Use in pregnancy and lactation
               3.13.6. Storage
               3.13.7. Special risk groups
         3.14. References


         4.1. Introduction
         4.2. Name and chemical formula of antidote
         4.3. Physico-chemical properties
         4.4. Pharmaceutical formulation and synthesis
         4.5. Analytical methods
               4.5.1. Identification and quantification of dantrolene
                       sodium and its formulation
               4.5.2. Quantification of dantrolene in body fluids
                High-performance liquid chromatography
         4.6. Shelf life
         4.7. General properties
         4.8. Animal studies
               4.8.1. Pharmacodynamics
                Effect on skeletal muscle
                Effects on other tissues
                Studies in malignant hyperthermia-
                                 susceptible pigs
               4.8.2. Pharmacokinetics
               4.8.3. Toxicology
                Acute toxicity
                Subacute toxicity
                Chronic toxicity
         4.9. Volunteer studies
               4.9.1. Administration and plasma concentrations
               4.9.2. Distribution
                Distribution to the fetus and
                                 newborn baby
               4.9.3. Elimination
               4.9.4. Human  in vitro pharmacodynamics
         4.10. Clinical studies - clinical trials
         4.11. Clinical studies - case reports

               4.11.1. Use in malignant hyperthermia
               Prophylaxis of malignant hyperthermia
               Prophylaxis of malignant hyperthermia
                                 during pregnancy
               4.11.2. Use in neuroleptic malignant syndrome
               4.11.3. Use in other drug-induced hyperthermia
         4.12. Summary of evaluation
               4.12.1. Indications
               Treatment of malignant hyperthermia
               Treatment of neuroleptic malignant
               Treatment of hyperthermia induced by
                                 muscle rigidity in poisoning
               4.12.2. Advised routes and doses
               Treatment of severe drug-induced
                                 hyperthermia, including malignant
               Prophylaxis of malignant hyperthermia
                                 prior to anaesthesia in susceptible
               4.12.3. Other consequential or supportive therapy
               4.12.4. Controversial issues and areas of insufficient
               4.12.5. Proposals for further studies
               4.12.6. Adverse effects
               Interaction with calcium antagonists
               4.12.7. Restrictions for use
         4.13. Model information sheet
               4.13.1. Uses as an antidote
               4.13.2. Dosage and route
               4.13.3. Precautions and contraindications
               4.13.4. Pharmaceutical incompatibilities and drug
               4.13.5. Adverse effects
               4.13.6. Use in pregnancy and lactation
               4.13.7. Storage
         4.14. References

         APPENDIX I    List of antidotes

         APPENDIX II   Principles for the evaluation of antidotes

         APPENDIX III  Proforma for monographs on antidotes for
                       specific toxic agents



    Dr D.N. Bateman, Department of Clinical Pharmacology, University of
    Newcastle, Newcastle-upon Tyne, United Kingdom

    Professor C. Bismuth, Hôpital Fernand Widal, Paris, France

    Dr R.E. Ferner, West Midlands Poisons Unit, Dudley Road Hospital,
    Birmingham, United Kingdom  (Joint Rapporteur)

    Dr T.J. Meredith, Department of Health, London, United Kingdom

    Dr H. Persson, Poison Information Centre, Karolinska Sjukhuset,
    Stockholm, Sweden  (Joint Chairman)

    Professor L. Prescott, Scottish Poison Information Service, The Royal
    Infirmary, Edinburgh, Scotland  (Joint Chairman)

    Dr M.-L. Ruggerone, Ospedale Niguarda, Centro Antiveleni, Milan, Italy

    Dr H. Smet, Centre Belge Anti-Poisons, Brussels, Belgium

    Dr U. Taitelman, National Poisons Information Centre, Rambam Medical
    Centre, Haifa, Israel

    Dr W. Temple, National Toxicology Group, Otago University Medical
    School, Dunedin, New Zealand  (Joint Rapporteur)

    Professor A.N.P. van Heijst, Bosch en Duin, The Netherlands

    Dr G. Volans, Poisons Unit, New Cross Hospital, London, United Kingdom

    Dr E. Wickstrom, National Poison Centre, Oslo, Norway


    Dr G. Olibet, Centro Antiveleni, Milan, Italy


    Dr J.-C. Berger, Health and Safety Directorate, Commission of the
    European Communities, Luxembourg

    Dr J.A. Haines, International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland

    Dr M. ten Ham, Pharmaceuticals Programme, World Health Organization,
    Geneva, Switzerland


         At a joint meeting of the World Federation of Associations of
    Clinical Toxicology and Poison Control Centres, the International
    Programme on Chemical Safety (IPCS), and the Commission of the
    European Communities (CEC), held at the headquarters of the World
    Health Organization in October 1985, the evaluation of antidotes used
    in the treatment of poisonings was identified as a priority area for
    international collaboration.  During 1986, the IPCS and CEC undertook
    the preparatory phase of a joint project on this subject.  For the
    purpose of the project an antidote was defined as a therapeutic
    substance used to counteract the toxic action(s) of a specified
    xenobiotic.  Antidotes, as well as other agents used to prevent the
    absorption of poisons, to enhance their elimination and to treat their
    effects on body functions, were listed and preliminarily classified
    according to the urgency of treatment and efficacy in practice.  With
    respect to efficacy in practice, they were classified as: (1) those
    generally accepted as useful; (2) those widely used and considered
    promising but not yet universally accepted as useful and requiring
    further research concerning their efficacy and/or their indications
    for use; and (3) those of questionable usefulness.  Additionally,
    certain antidotes or agents used for specific purposes were considered
    to correspond to the WHO criteria for essential drugs (see Criteria
    for the Selection of Essential Drugs, WHO Technical Report Series 722,
    Geneva, 1985).

         A methodology for the principles of evaluating antidotes and
    agents used in the treatment of poisonings and a proforma for
    preparing monographs on antidotes for specific toxins were drafted
    (Appendices II and III respectively).

         Monographs are being prepared, using the proforma, for those
    antidotes and agents provisionally classified in category 1 as regards
    efficacy in practice.  For those classified in categories 2 and 3,
    where there are insufficient data or controversy regarding efficacy in
    practice, it was agreed that further study was necessary. 
    Accordingly, several were selected for initial review and evaluation,
    among which were naloxone as an antagonist for opioids, flumazenil as
    a benzodiazepine antagonist and dantrolene for malignant hyperthermia.

         The review and evaluation of these antidotes was initiated at a
    joint meeting of the IPCS and the CEC, organized by the Northern
    Poisons Unit and held at the Medical School of the University of
    Newcastle-upon-Tyne, United Kingdom, 13-17 March 1989.  In preparation
    for this meeting, monographs were drafted, using the proforma, on
    naloxone by Dr D.N. Bateman, on flumazenil by Dr A. Brovard and
    Professor C. Bismuth and on dantrolene by Dr H. Smet and Professor C.
    Bismuth.  The draft document on naloxone was reviewed by a working
    group consisting of Professor L.F. Prescott (Chairman), Dr W. Temple
    (Rapporteur), Dr D. Bateman, Dr M. Ten Ham, Dr A.N.P. van Heijst, Dr
    G.N. Volans and Dr E. Wickstrom.  The draft documents on flumazenil

    and dantrolene were reviewed by a working group consisting of Dr H.
    Persson (Chairman), Dr R.E. Ferner (Rapporteur), Dr J.-C. Berger,
    Professor C. Bismuth, Dr G. Olibet, Dr M.-L. Ruggerone, Dr H. Smet and
    Dr U. Taitelman.

         Following the meeting further drafting work was undertaken by the
    authors, with the assistance of Drs R.E. Ferner, B. Britt (Department
    of Anaesthesia, Faculty of Medicine, University of Toronto, Canada),
    and T. Fagerlund (Institute of Medical Genetics, University of Oslo,
    Norway) in the redrafting of the dantrolene monograph.  Draft texts
    were further revised by the series editors (Dr T.J. Meredith, Dr D.
    Jacobsen, Dr J.A. Haines, and Dr J.-C. Berger), who also prepared an
    introduction to the series.  This introduction summarizes the results
    of the preparatory phase and indicates the volumes currently planned
    for this series.  The efforts of all who helped in the preparation and
    finalization of this volume are gratefully acknowledged.


    BZD     benzodiazepine
    CAT     computer-assisted tomography
    CNS     central nervous system
    GABA    gamma-aminobutyric acid
    GLC     gas-liquid chromatography
    HIV     human immunodeficiency virus
    HPLC    high-performance liquid chromatography
    LSD     lysergic acid diethylamide
    RIA     radio-immunoassay
    TLC     thin-layer chromatography
    UV      ultraviolet


         Antidotes play a vital role in the treatment of poisoned
    patients.  Good supportive care, directed particularly at the cardiac
    and respiratory systems, and the use of elimination techniques when
    indicated, enable the majority of poisoned patients to make a full
    recovery.  However, in certain circumstances the use of antidotes can
    be life-saving, and in other circumstances the use of antidotes may
    reduce morbidity as well as medical and other resources required in
    the care of a patient.  In areas remote from hospital care, and
    particularly in developing countries where facilities for supportive
    care outside hospital are often limited, the availability of certain
    antidotes is even more essential for the successful treatment of a
    poisoned patient.

         However, there remains controversy about the clinical efficacy
    and indications for use of many of the antidotes conventionally
    employed in the treatment of poisoning.  There is also sometimes
    difficulty in obtaining antidotes in an emergency situation,
    particularly if the substance in question is not available as a
    pharmaceutical preparation.

         The need for an international evaluation of the clinical efficacy
    of antidotes and other substances used in the treatment of poisoning
    was first recognized at a joint meeting of the World Federation of
    Associations of Clinical Toxicology Centres and Poisons Control
    Centres, the International Programme on Chemical Safety (IPCS) and the
    Commission of the European Communities (CEC), held at WHO
    headquarters, Geneva, 6-9 October 1985.  At the same time, the need to
    encourage the more widespread availability of those antidotes that are
    effective was also recognized.  As a result, a joint IPCS/CEC project
    was subsequently initiated to address these problems.

         In a preparatory phase of the project, an antidote was defined
    for working purposes as a therapeutic substance used to counteract the
    toxic action(s) of a specified xenobiotic.  A preliminary list of
    antidotes for review, as well as of other agents used to prevent the
    absorption of poisons, to enhance their elimination and to treat their
    effects on body functions, was established.  For the purposes of the
    review process, antidotes and other substances were classified
    according to the urgency with which treatment with the antidote was
    thought on current evidence to be required and the (currently judged)
    clinical efficacy of the antidote in practice.  Those corresponding to
    the WHO concept of an essential drug were designated as such.  Some
    have already been incorporated into the WHO list of essential
    drugsa.  Antidotes and similar substances for veterinary use were

    a  WHO (1988) Use of Essential Drugs. Model list of essential drugs
       (fifth list). Third Report of the WHO Expert Committee. WHO
       Technical Report Series 770, Geneva World Health Organization.

    also listed.  A methodology on the principles for evaluation of
    antidotes and other agents used in the treatment of poisonings was
    developed and this has subsequently been used as a framework for
    drafting monographs on specific antidotes.  The list of antidotes and
    other agents established as a result of the preparatory phase and the
    preliminary classification is given in Appendix I.  The principles for
    evaluation are detailed in Appendix II.

         Early during the course of the preparatory phase, it became
    apparent that the availability of antidotes differed from one country
    to another.  Problems of availability fell into three interrelated
    categories, namely:

    *    scientific, technical and economic aspects;

    *    regulatory and administrative requirements;

    *    geospatial and time considerations.

         Problems of availability of antidotes used in the treatment of
    poisonings were therefore examined by an IPCS/CEC Working Group,
    hosted by the Norwegian National Poisons Information Centre and held
    in Oslo, 20-22 June 1988.  The record of this meeting is given in
    ICS/88.44.  In preparation for this meeting, a preliminary survey was
    undertaken of selected poisons control centres in order to identify
    more precisely the practical difficulties encountered in obtaining
    antidotes.  The survey showed that, in general, poisons centres in
    industrialized countries had few problems in obtaining most antidotes,
    although lack of suitable preparations/importers/manufacturers
    together with administrative difficulties did hinder access to certain
    antidotes.  In contrast, centres in developing countries reported many
    problems in obtaining even those antidotes that are readily available

         A report was prepared by the IPCS/CEC Working Group setting out
    the problems associated with the availability of antidotes and
    suggesting ways in which the availability of antidotes might be
    ensured for the treatment of poisoned individuals.  In due course, it
    is intended that this report will be brought to the attention of all
    relevant national drug regulatory and importation authorities,
    pharmaceutical manufacturers, distributors of pharmaceutical
    materials, and all poisons control centres.  The IPCS Guidelines for
    Poisons Control summarize the problems and issues of availability
    identified by the Working Groupb.

    b  WHO (in press) - Guidelines for Poisons Control, Part II, section
       6 Geneva, World Health Organization

    Aspects of the evaluation of antidotes

         The development and evaluation of substances to counteract the
    toxic action(s) of a xenobiotic is principally a task for the
    scientific community, particularly those working in experimental
    pharmacology, toxicology and clinical medicine.  The efficacy of a
    substance intended for use as an antidote must first be demonstrated
    in an appropriate animal model.  The next step, demonstration of
    efficacy in humans, it is often more difficult because there is rarely
    an opportunity for controlled clinical trials.  Even if a substance
    is shown to be effective as an antidote, the potential intrinsic
    toxicity of the substance also needs to be considered prior to its
    more widespread use, and, as with all drugs, the possibility of an
    adverse drug reaction should be considered.  A clinician is more
    likely to be prepared to use a relatively "non-toxic" antidote (even
    one whose efficacy has still to be established with certainty) than
    one with intrinsic toxicity.  An antidote which is potentially toxic
    should only be used if it is therapeutically effective and the
    indication for use is clear.  Although possible long-term adverse
    effects and chronic toxicity need to be considered, they are usually
    of less consequence than for an ordinary pharmaceutical agent because
    treatment with an antidote is rarely required more than once in any
    particular individual.  A final consideration in the use of an
    antidote is that increased toxicity should not result from
    mobilization of the toxin from tissue stores or from changes in tissue

    The concept of relative "efficacy" of antidotes

         It is important that clinicians employing antidotes in the
    treatment of poisoned patients recognize that the clinical "efficacy"
    of antidotes varies considerably.  On the one hand there are antidotes
    whose clinical effect is both rapid and dramatic.  Examples would be
    naloxone or flumazenil, which act as very specific competitive
    antagonists at opioid and benzodiazepines receptors, respectively.

         On the other hand, there are antidotes that are able to counter
    only some of the toxic effects of a particular compound; if the dose
    of the compound in question is sufficiently high then the patient is
    likely to die despite the use of an antidote.  Chelating agents
    provide good examples of antidotes that fall into this category of
    efficacy.  Nevertheless, chelating agents have a valuable role to play
    in the treatment of heavy metal poisoning, and many are recommended
    for this purpose in volume V of this series.

         Some agents are loosely termed antidotes even though they may
    have little or no true antidotal effect; they may nonetheless form
    valuable adjuncts to treatment.  Diazepam, used in the treatment of
    organophosphate poisoning (volume IV), is one such example.

    Provisional list of volumes in the IPCS/CEC antidotes series

         It is intended that the IPCS/CEC series of monographs on
    antidotes will cover all antidotes that are commonly employed - or
    which have been proposed for use - in the treatment of human
    poisoning.  Once this aim has been achieved, it is intended that the
    volumes will be periodically updated in order to meet the needs of
    health care professionals.  At present, the proposed volumes for this
    series include:

    Volume 2

    Evaluation of antidotes for cyanide poisoning:

    *    oxygen
    *    sodium thiosulfate
    *    hydroxocobalamin
    *    dicobalt edetate
    *    amyl nitrite
    *    sodium nitrite
    *    4-dimethylaminophenol
    *    antidotes to methaemoglobin-forming agents (methylene blue,
         toluidine blue)
    *    analytical methods for cyanide alone and in combination with
         cyanide antidotes

    Volume 3

    Evaluation of antidotes for paracetamol poisoning

    *    overview
    *    N-acetylcysteine
    *    methionine

    Volume 4

    Evaluation of antidotes for organophosphate poisoning

    *    overview
    *    atropine
    *    diazepam
    *    obidoxime
    *    pralidoxime

    Volume 5

    Evaluation of chelating agents for heavy metal poisoning

    *    overview
    *    deferoxamine
    *    prussian blue
    *    trientine
    *    calcium disodium edetate
    *    DTPA
    *    DMPS
    *    DMSA
    *    dimercaprol
    *    penicillamine and N-acetyl penicillamine

    Volume 6

    Antidotes for methanol and ethylene glycol poisoning.

    Volume 7

    Antidotes for amatoxin, gyrometrine and isoniazid poisoning

    Volume 8

    Evaluation of the various pharmaceutical substances used for enhanced
    elimination and prevention of absorption.

    Further volumes are planned for:

    *    General antidotes and sorbents
    *    Antidotes based on immunotoxicology

    International evaluation process

         Experts are requested by the IPCS to prepare draft monographs on
    specific antidotes or agents, or on specific aspects associated with
    their therapeutic use.  Original literature references must be used
    according to the criteria established for Environmental Health
    Criteria documents.  In order to ensure that monographs are written
    according to agreed standards, a common format has been established
    following the methodology on principles for evaluation of antidotes
    (Appendix II) and the guidelines to authors (Appendix III).  The
    series editors examine the drafts to ensure that they conform to the
    standard format and are of acceptable quality for peer review.  For
    certain volumes a guest editor is also appointed.  The IPCS sends the
    drafts to selected experts for comment and for possible additional

    information.  A working group of authors and experts in the field is
    then convened by the IPCS and CEC.  The task of this group is to:

    (i)     examine the literature referred to in the monographs for its
            relevance, including case data experience;

    (ii)    identify any gaps in knowledge or scientific unknowns;

    (iii)   make an evaluation of the clinical efficacy of the antidote
            for a particular poisoning or pathological condition resulting
            from the poisoning;

    (iv)    provide guidance on the treatment regimens, under various
            conditions of use of the antidote, including, where
            appropriate, field and primary health care use, advise on the
            accompanying supportive care, and give particular attention to
            paediatric doses, contraindications and special

         Following the working group meeting further drafting may need to
    be undertaken by the original author in consultation with the series
    and guest editors.  An overview chapter summarizing the issues and
    giving the evaluation of a series of antidotes for specific types of
    poisoning cases is drafted by the editors or invited experts.  The
    IPCS and CEC may convene a further editorial meeting to finalize the
    monographs for a particular volume and to approve the overview
    chapter.  The volume is then processed by the WHO editor for
    publication by Cambridge University Press.

    2.  NALOXONE

    2.1  Introduction

         Naloxone is an opioid antagonist acting at all three types of
    opioid receptors.  It appears devoid of agonist activity (Martin,
    1976).  Naloxone is indicated in the treatment of opiate poisoning.

         Although naloxone has also been reported to be of benefit as an
    antidote in benzodiazepine (BZD) poisoning (Bell, 1975), other workers
    failed to demonstrate an effect in a double-blind study of
    diazepam-induced sedation (Christensen & Huttel, 1979).  However,
    Jordan (1980) demonstrated some reversal of diazepam-induced
    respiratory depression by naloxone.  Thus there is a need for further
    controlled studies, particularly in cases of poisoning.

         Naloxone has also been claimed to have an effect on
    ethanol-induced central nervous system (CNS) depression, and in one
    study appeared to cause an improvement in 20% of treated cases
    (Jefferys et al., 1980).  However, this finding has not been confirmed
    by other workers (Handal et al., 1983; Nuotto et al., 1984).

         The possible beneficial effects of naloxone in non-opiate
    poisoning probably reflect the involvement of endogenous opioids in
    the depressant action of some non-opioid drugs (McNicholas & Martin,

    2.2  Name and Chemical Formula

    Empirical formula: C19 H21 NO4
    Relative molecular mass: 327
    CAS number:  465-65-6
    Trade names: Narcan, Nalone, Narcanti (Du Pont Pharmaceuticals)

         Naloxone is available for clinical use as the hydrochloride salt,
    which may be anhydrous (CAS-357-08-4) or contain 2 molecules of water
    of hydration (CAS 51481-60-8).  The relative molecular mass of the
    free base is 327.37 and of the anhydrous salt 363.84.

    Conversion table:  1 g = 3.1 mmol
                       1 mmol = 327.4 mg
                       1 mg/ml = 3.1 mmol/l
                       1 mmol/l = 0.33 mg/ml

    The molecular structure of naloxone hydrochloride is shown below.


    2.3  Physico-chemical Properties

         Naloxone hydrochloride has a melting range of 200-205 °C.  It is
    soluble in water, dilute acids and strong alkalis, and is slightly
    soluble in alcohol but practically insoluble in ether.  Aqueous
    solutions are acidic (pH 3 to 4.5) (United States Pharmacopeia, 1980)
    and an 8.08% solution in water is isotonic with serum (Hassan et al.,
    1985).  A 25% solution of naloxone hydrochloride rotates light between
    -170 and -181.  Naloxone crystals from ethyl acetate have a specific
    optical rotation at 20 °C ([alpha]D20; 9.3 g/l chloroform) of
    -194.5 ° (Windholz, 1983).

         Naloxone has a pKa (20 °C) values for the nitrogen and phenolic
    H groupings of 7.94 and 9.44, respectively (Kaufman et al., 1975).

         On drying at 105 °C, the anhydrous form loses not more than 0.5%
    and the hydrated form not more than 11% of its weight.

         The solution for injection is made up in water and should be
    protected from light.  Naloxone can be diluted in 0.9% saline or 5%
    dextrose and should then be used within 24 h.  It should not be mixed
    in solutions containing metasulfite, metabisulfite, or long-chain or
    high relative molecular mass anions, or in those with an alkaline pH.

    2.4  Pharmaceutical Formulation and Synthesis

         Three synthetic routes for the production of naloxone have been
    reported (Hassan et al., 1985).  Oxymorphone is a starting point for
    two of the synthetic processes and 14-hydroxycodeinone for the third.

    Noroxymorphone hydrochloride is a potential impurity from the
    manufacturing process.

    2.5  Analytical Methods

    2.5.1  Quality control

         Naloxone hydrochloride can be assayed by gas chromatography with
    flame ionization detection (United States Pharmacopeia, 1980).

    2.5.2  Identification

         About 150 mg of the unknown substance is dissolved in 25 ml of
    water and a few drops of 6N ammonium hydroxide are added.  Three 5-ml
    portions of chloroform are used for extraction and the extract is
    filtered.  The filtrate is collected, evaporated to dryness using a
    steam bath, and dried at 105 °C for one hour.  The infrared absorption
    spectrum of a 1-in-50 solution of the residue obtained in chloroform
    will have maxima at the same wavelengths as those of a similar
    solution of naloxone reference standard.

         The addition of one drop of ferric chloride solution to 1 ml of
    a 1-in-100 solution of naloxone hydrochoride results in a clear
    purplish-blue colour.

    2.5.3  Quantification of the antidote

         Assay methods for naloxone in biological fluids employing
    gas-liquid chromatography (GLC) (Meffin & Smith, 1980),
    radio-immunoassay (RIA) (Berkowitz et al., 1975; Hahn et al., 1983)
    and high-performance liquid chromatography (HPLC) (Asali, 1983; Terry
    et al., 1984) have all been reported.  The GLC method involves
    derivatization and the specific antibody for the RIA is not widely
    available.  The HPLC methods reported appear sensitive and
    reproducible, and are therefore probably the methods of choice.

    2.5.4  Analysis of toxic agents

         In the majority of cases in which naloxone is used as an
    antidote, there is no way of measuring the level of the opioid poison. 
    Present assay techniques for many opiates are difficult, and RIA
    suffers from lack of specificity in many cases.  Some opiates, e.g.,
    morphine, also appear to have active metabolites (Bodd et al., 1990).
    The most widely used method for opioid detection is RIA of urine.

    2.6  Shelf-life

         The shelf-life of naloxone for intravenous injection in temperate
    countries is 3 years and has a similar length in tropical countries.

    2.7  General Properties

         Naloxone is a specific opioid antagonist (Martin, 1976) and it is
    for this reason that it is used in the treatment of poisoning.  There
    are reports that it may reverse the central effects of ethanol and BZD
    poisoning in man.  However, these are experimental uses that remain
    unproven, and any observed effects probably reflect the involvement of
    endogenous opioids in the nonspecific depressant action of those
    agents (McNicholas & Martin, 1984).

    2.8  Animal Studies

    2.8.1  Pharmacodynamics

         Naloxone is a competitive antagonist at opiate receptors, and
    appears to be effective at all three types of receptor (mu, kappa and
    sigma) (Martin, 1976).  It does not produce habituation in animal or
    human models of opiate tolerance and appears to be free of agonist
    activity in most laboratory test models (Jasinski, 1967; McNicholas &
    Martin, 1984).  It produces a parallel shift in the  in vitro dose-
    response effects of pure agonist opioids, such as morphine, and
    partial agonists, such as pentazocine (Smits & Takemori, 1970),
    buprenorphine and dextropropoxyphene.

         Since the range and relative quantities of opioid receptors vary
    in different animal tissues, a range of concentrations of naloxone is
    required to antagonize opioid effects in different test systems. 
    Confusion has arisen as to whether naloxone is a pure antagonist. 
    This is because some opioid receptors act as modulators and enhance
    nociceptive stimuli.  Thus, in some animal models naloxone appears to
    possess agonist effects, but this is in fact incorrect (Sawynok et
    al., 1979).  Naloxone has also been observed in some experiments to
    antagonize the antinociceptive effects of some non-opiate drugs. 
    Again it seems likely that this reflects an involvement of opioid
    receptors in the mechanism of action of these drugs (Sawynok et al.,
    1979). However, in a recent study in rats, Kotlinska & Langwinski
    (1990) failed to find any evidence for the participation of the opioid
    system in the mediation of acute ethanol effects in rats.

         Naloxone has been reported to either decrease or have no
    influence on barbiturate-induced anaesthesia.  This paradox may be a
    result of the dose-response relationship of the effects of naloxone,
    which at high doses may have a potentiating effect (Sawynok et al.,
    1979).  Naloxone has some activity as a GABA antagonist and may thus
    have convulsant activity.  However, this is likely to be at much
    higher concentrations that those encountered clinically (Dingledine et
    al., 1978), since in mice a dose of 100 mg/kg was required to produce

         Naloxone has also been shown to have a number of biochemical
    effects in the rat, including inhibition of lipolysis and a subsequent
    increase in circulating free tryptophan (Badawy et al., 1983).

    2.8.2  Pharmacokinetics

         Naloxone appears to be readily absorbed after oral administration
    but undergoes extensive first-pass hepatic metabolism, which results
    in a very low bioavailability (Misra, 1978).  Studies of the
    pharmacokinetics of intravenous naloxone have been performed in a
    variety of animal species including the rat, rabbit and dog.  Many of
    these studies are based on radio-immunoassay of naloxone.

         The serum concentration of naloxone found 5 min after injection
    was similar (5 mg/kg) in the rat and the dog (Ngai et al., 1976; Pace
    et al., 1979).  The half-life of the parent drug in the rat (30 min)
    was approximately half that in the dog (71 min).

         Ngai et al. (1976) also examined the brain:serum ratio of
    naloxone and found this to vary in the rat between 2.7:1 and 4.6:1.
    Intravenously administered naloxone acts rapidly on the brain.  The
    brain:serum ratio was higher, however, when the naloxone was
    administered subcutaneously.  These workers also studied, in a
    parallel group of animals, the distribution of morphine and noted that
    the brain:serum ration was 1:10.

         The initial distribution of naloxone may account for the rapid
    onset of its reversal of opiate effects when it is given
    intravenously.  The major metabolite of naloxone is the glucuronide.
    Naloxone-3-glucuronide has been found, for example, in the rabbit
    (Fujimoto, 1969).  A conjugated 6-hydroxy product of naloxone,
     N-allyl-14-hydroxy-7,8-dihydronormorphine-3-glucuronide was
    identified in the chicken by Fujimoto (1969); this conjugate was also
    identified in the rabbit by Weinstein et al. (1974) but only in small

         The relatively short action of naloxone appears to result from
    the ease with which it enters the brain after intravenous dosing and
    the subsequent rapid redistribution, elimination and consequent fall
    in brain naloxone levels (Berkowitz, 1976).

         Hydroxylated metabolites of naloxone appear to possess narcotic
    antagonist activities, but their potencies are much weaker than the
    parent compound.  Thus they are unlikely to be of significance in view
    of the small amounts produced (Fujimoto et al., 1975).

         The distribution of naloxone has not been found to be altered by
    a 25-fold range of morphine concentration in the rat (Fishman et al.,

    2.8.3  Toxicology

         Acute toxicity studies with naloxone have been performed in mice,
    rats and dogs.  The LD50 for intravenous administration was 150
    mg/kg in mice, 109 mg/kg in rats and 80 mg/kg in dogs (Social Welfare
    Board, 1976).  For 24-h-old rats the LD50 was 260 mg/kg when given
    subcutaneously (Blumberg et al., 1966).  The maximum nontoxic
    subcutaneous dose in rats was found to be of the order of 50 mg/kg
    (Blumberg et al., 1966).  This dose was tolerated for 24 days, whereas
    200 mg/kg resulted in tremor, convulsions and salivation.

         Daily doses of 0.2 mg/kg given intravenously to dogs for 16 days
    and 5 mg/kg given subcutaneously to monkeys for 30 days caused no
    toxicity.  However, a subcutaneous dose of 20 mg/kg resulted in
    lethargy and tremor in monkeys.

         No teratogenic effects were observed in mice, rats or rabbits
    when naloxone was given parenterally over the period of organogenesis
    (Social Welfare Board, 1976).  No studies on mutagenicity have been

    2.9  Volunteer Studies

         Studies of the pharmacokinetics and pharmacodynamics of naloxone
    have been performed in volunteers.

    2.9.1  Pharmacokinetics

         Using an RIA assay, the pharmacokinetics of naloxone were found
    to fit a two-compartment model, with a rapid distribution phase and a
    slower elimination phase, having a half-life of 64 min (Ngai et al.,
    1976).  More recent studies using HPLC to assay naloxone suggest that
    the apparent volume of distribution, half-life and clearance all show
    differences within groups of normal volunteers.  Thus Aitkenhead et
    al. (1984) reported a mean apparent volume of distribution at steady
    state of 3.65 l/kg (range 1.43-7.05 l/kg) and a mean half-life of
    151.2 min (range 47.1-313.2 min).  Using an HPLC assay, Goldfrank et
    al. (1986) found less variability in patients (half-life 28-55 min).

         The kinetics of naloxone in infants appear similar to those in
    adults (Stile et al., 1984).

         Orally administered radiolabelled naloxone undergoes extensive
    first-pass metabolism in normal subjects (Fishman et al., 1973). 
    After intravenous administration, most (70%) of the radioactivity was
    recovered in urine, the major part of which was conjugated as the
    glucuronide.  In addition other metabolites were found in small
    quantities, i.e. the glucuronide conjugates of 7,8-dihydro-14-hydroxy-
    normorphine, and  N-allyl-7,8-dihydro-14-hydroxy-normorphine
    (Weinstein et al., 1971).

         As a consequence of the high hepatic clearance of naloxone and
    relatively weak agonist activity of its metabolites, it is unlikely
    that dose adjustments would be necessary in cases of renal failure. 
    Naloxone is only 54% protein-bound in adult plasma (61.5% in fetal
    plasma), and this binding is not concentration-dependent over the
    range 9 ng/ml to 2.5 µg/ml (Asali & Brown, 1984).  Thus protein-
    binding interactions seem unlikely.

         The elimination of naloxone might be altered in patients with
    liver disease, but no studies appear to have been performed.

    2.9.2  Pharmacodynamics

         Studies have been conducted on the duration of action and potency
    of naloxone in reversing respiratory depression induced by morphine
    (intravenous doses of 5 mg plus 10 mg) in volunteers (Kaufman et al.,
    1981).  The effect of naloxone against this therapeutic dose of
    morphine reached a peak at around 30 min, which was equatable with the
    probable peak in brain concentration.  It should be noted that the
    times of onset and peak effect of naloxone differed.  The duration of
    action of naloxone appeared to be about 1.5 h in this experimental

         Johnstone (1974) examined the effects of an infusion of naloxone
    in volunteers who had received 2 mg/kg morphine intravenously and been
    anaesthetized for 5 h.  Intravenous naloxone given to these volunteers
    at a rate of 40 µg/kg over a 10-h period reversed the central
    depressant effects of morphine on respiratory function (measured by
    CO2 responsiveness) and higher functions (assessed by a vigilance
    test).  No tachyphalaxis to the effects of naloxone was observed over
    this period (Johnstone et al., 1974).

         It has been suggested that ethanol may exert some of its effects
    via the endogenous opiate system, as illustrated by the study by
    Jeffferys et al. (1980) and Jeffcoate et al. (1979) where naloxone was
    found to antagonize some of the ethanol effects. However, these
    findings could not be confirmed by Handal et al. (1983) or Nuotto et
    al. (1984).  In the latter study, the effect of naloxone on ethanol-
    induced impairment of psychomotor performance was first studied in two
    placebo-controlled, double-blind, cross-over trials in 17 healthy male
    volunteers.  The main conclusion was that naloxone (intravenous doses
    of 0.4 plus 2 mg) had no significant antagonizing effects on the
    impairment induced by ethanol (1.5 g/kg).  However, a slight but
    significant effect on ethanol-induced nystagmus was noted.  A placebo-
    controlled, double-blind study was subsequently conducted on male
    alcoholics admitted for acute ethanol intoxication (the mean blood
    ethanol level was 2.9 g/l (64 mmol/l)). In this case, neither naloxone
    (intravenous doses of 0.4 plus 2 mg; n=11) nor saline (n=7) had any
    effect, as judged from a clinical inebriation test (Nuotto et al.,

    2.9.3  Effects of high doses of naloxone

         Naloxone has been administered to healthy volunteers at dose
    levels of 0.3-4 mg/kg.  These high dose levels produced dose-dependent
    dysphasia and memory impairment.  In addition, increases in blood
    pressure and respiratory rate were noted, together with increases in
    cortisol and growth hormone levels (Cohen et al., 1983).  These
    findings have been used to support the hypothesis that endogenous
    opioids play a normal regulatory physiological role, but obviously
    have potential therapeutic implications if large doses of naloxone are
    used to treat poisoned patients.

    2.10  Clinical Studies - Clinical Trials

         Naloxone has been investigated in clinical studies on both
    patients who have received a therapeutic dose of an opiate (see
    section 2.9) and those who have been poisoned with opiates.  Since
    naloxone is a competitive antagonist, the dose required to reverse the
    clinical effects of a specific opiate will depend on the dose of the
    opiate, its duration of action, and its pharmacological properties,
    particularly whether it has partial agonist activity or shows
    selectivity at one type of opioid receptor subgroup (Martin, 1976).

    2.10.1  Effects in therapeutic use of opioids

         An alternative method of studying the response to naloxone was
    reported by Drummond et al. (1977). They studied patients who had been
    anaesthetized and had received the synthetic opiate fentanyl. 
    Naloxone produced a dose-dependent increase in respiratory function
    (measured as minute volume or respiratory rate) with intravenous doses
    of 0.1, 0.2 and 0.4 mg.

         Hatano et al. (1975) reported an open study on 80 patients
    undergoing a variety of surgical procedures including cardiopulmonary
    bypass.  Premedication included pethidine (meperidine) and induction
    was achieved with pentazocine and diazepam.  The doses of pentazocine
    in males were 2 mg/kg and females 1.5 mg/kg, and those of diazepam
    were 0.4 and 0.3 mg/kg, respectively.  The authors used a stepwise
    increment of naloxone (0.2-mg intravenous boluses) to achieve reversal
    of the opiate effect of pentazocine at the end of the operative
    procedure and noted a stepwise reversal of the opiate effects in their
    patients as the opiate dose was increased (the average total dose
    given was 2.5 mg/kg body weight).

         The duration of action of naloxone in reversing the effects of
    morphine (5 or 10 mg, intramuscular) in patients recovering from
    surgery is relatively short (Longnecker et al., 1973).  The authors
    suggested that the use of a combination of intravenous and
    intramuscular naloxone might be an appropriate regimen in the post-
    operative situation;  this has also been suggested for the treatment
    of acute overdoses in heroin addicts (see sections 2.12.2 & 2.13.2).

    2.10.2  Effects in acute opioid poisoning

         Two important studies have demonstrated the efficacy of naloxone
    in reversing opiate poisoning.  Evans et al. (1973) reported a study
    in which naloxone (0.4-1.2 mg, intravenous) resulted in recovery of
    consciousness within 1-2 min in nine patients with a history of opiate
    ingestion.  This was associated with improvement in respiratory
    function in the six patients in whom this could be measured with
    minute volume and respiratory rate.  The opiates taken by these
    patients were reported as dipipanone (3), pethidine (2),
    dihydrocodeine (2), pentazocine (1) and heroin (1).  In contrast, none
    of 13 patients overdosed with a variety of other central nervous
    system depressants showed improvement after having been given a total
    intravenous dose of 1.2 mg naloxone.  This rapid and clear benefit of
    therapy was also reported by Buchner et al. (1972), who studied the
    effects of naloxone (0.005 to 0.01 mg/kg) in 10 children with
    methadone poisoning.  Although they did not study a control group,
    they did confirm the presence of methadone in biological fluids in
    some of their patients.  These authors stress the importance of an
    adequate period of observation for patients poisoned with long-acting
    opiates and the necessity of repeated doses of naloxone.

         Since the onset of the effects of naloxone is so rapid, it has
    proved relatively easy to confirm its effectiveness in opiate
    poisoning at restoring consciousness and improving respiration. 
    Further extensive clinical trials in opiate poisoning have, therefore,
    not been performed.

         Henry & Volans (1984) have stressed the importance of classifying
    drugs correctly as opioids.  A list of opioids is a useful reminder
    (Table 1) that agents such as loperamide and diphenoxylate may produce
    significant systemic toxicity in overdose.

         One particular aspect of naloxone use that requires consideration
    is that of the most appropriate dosage regimen.  Early human studies
    confirmed that the duration of action of naloxone was shorter than
    might have been expected from its plasma half-life (Berkowitz et al.,
    1975).  The long duration of action of some opiates is also a factor
    in the need to repeat the initial dose of naloxone in poisoned
    patients (Gober et al., 1979).  As an alternative to repetitive
    dosing, several research workers have suggested that intravenous
    loading doses followed by a steady-state infusion of the drug would be
    appropriate both in children (Gourlay & Coulthard, 1983; Tenenbein,
    1984) and in adults (Bradberry & Raebel, 1981; Goldfrank et al., 1986)
    suffering opiate poisoning.  These regimens have appeared safe and
    effective in clinical use, but do not obviate the need for close
    monitoring during treatment of respiratory function, conscious level
    and cardiovascular function.  It is important to remember that some
    synthetic opioids, e.g., dextropropoxyphene, have been reported to
    produce toxic effects at high doses, which are not reversible by

    naloxone (Barraclough & Lowe, 1982).  These effects may be due to a
    direct action of dextropropoxyphene on cardiac cell membranes.

    Table 1.  Alphabetical list of opioid drugsa


    Alletorphine                    Levorphanol
    Alphaprodine                    Loperamide
    Anileridine                     Meptazinol
    Azidomorphine                   Methadone
    Bezitramide                     Metofoline
    Buprenorphine                   Morphine
    Butorphanol                     Nalbuphine
    Codeine                         Norpipanone
    Dextromoramide                  Opium
    Dextropropoxyphene              Oxycodone
    Diamorphine (Heroin)            Oxymorphone
    Difenoxin                       Papaveretum
    Dihydrocodeine                  Pentazocine
    Diphenoxylate                   Pethidine (Meperidine)
    Dipipanone                      Phenadoxone
    Ethoheptazine                   Phenazocine
    Ethylmorphine                   Phenoperidine
    Etorphine                       Piminodine
    Fentanyl                        Piritramide
    Hydrocodone                     Thebacon
    Hydromorphone                   Tilidate
    Ketobemidone                    Tramadol
    Levomethadyl                    Trimeperidine

    a  From Martindale (1982).  Some of these drugs may be marketed as
       part of a combination preparation.

    2.11  Clinical Studies - Case Reports

         Individual published case reports have confirmed efficacy for the
    majority of opiates (Handal et al., 1983).  In patients who are
    narcotic addicts, naloxone may precipitate features of acute opiate
    withdrawal.  Doses of up to 20 mg naloxone have been used in children
    without associated adverse effects (Handal et al., 1983).

         If patients with acute renal failure are given morphine over
    several days for various reasons (e.g., for sedation while on a
    respirator), opioid toxicity may occur due to accumulation of the
    active metabolite morphine-6-glucuronide, which is renally excreted
    (Bodd et al., 1990).  In such cases, the opioid toxicity may last for
    up to two weeks after the cessation of morphine therapy, and the
    patient will need naloxone infusion in order to avoid respiratory

    2.11.1  Naloxone in clonidine poisoning

         Clonidine hydrochloride is a central and peripheral
    alpha-adrenergic antagonist that is still used in the treatment of
    hypertension. It has also been suggested for the treatment of opiate
    withdrawal (Gold et al., 1980). The mechanism for this effect and for
    the claimed effect of naloxone in some cases of clonidine poisoning
    (North et al., 1981; Kulig et al., 1982) is not clear, but the
    involvement of endogenous opioids has been suggested.  However, the
    effect of naloxone in clonidine poisoning could not be confirmed by
    Banner et al. (1983).  In a retrospective study of 47 consecutive
    children admitted for clonidine poisoning (Wiley et al., 1990), only
    3 out of the 19 given naloxone showed a temporary response. One child
    had an episode of severe hypertension associated with naloxone
    administration (0.1 mg/kg). Thus, there is no clear documentation for
    the beneficial effect of naloxone in clonidine poisoning.

    2.12  Summary of Evaluation

    2.12.1  Indications

         Naloxone has been reported to significantly antagonize acute
    opioid toxicity and opioid effects within anaesthesia. Its high
    therapeutic index and possible beneficial effect in other poisonings
    allow for diagnostic use in critically ill patients when opioid
    poisoning may be a differential diagnosis.

    2.12.2  Advised routes and dose

         In patients with  definite opiate poisoning, naloxone should be
    given by the intravenous route until an improvement in conscious level
    and respiration is observed.  This may involve the administration of
    several milligrams of naloxone if partial opioid agonists are given,
    but 0.8-1.2 mg is usually sufficient in morphine or heroin poisonings. 
    It is important to stress that a pharmacologically active dose of
    naloxone in opiate poisoning may be more than that normally
    recommended in anaesthetic practice.

         In patients with  suspected opiate poisoning, an intravenous
    injection of up to 2 mg naloxone should be administered and the
    patient's response closely monitored.  If there is improvement in
    conscious level, respiratory rate or cardiovascular parameters,
    further doses of naloxone should be administered.  The effect of
    naloxone should be visible within 1 to 2 min after administration.

         Once a patient has regained consciousness, it is necessary to
    continue to monitor respiration and cardiovascular status at regular
    intervals.  In the patient who has taken a large opiate overdose or an
    overdose of a long-acting opiate, it may be necessary to repeat dosing
    with naloxone.  This may be conveniently done by establishing an
    intravenous infusion of naloxone.  A guide to the required dosage has

    been suggested by Goldfrank et al. (1986).  From studies of the
    pharmacokinetics of naloxone in patients suffering opiate poisoning,
    they calculated that an hourly infusion of two-thirds of the dose
    required initially to reverse the effects of the opiate would maintain
    naloxone levels at approximately those present 30 min after the
    initial bolus administration.

         Another approach to opioid poisoning that may sometimes be
    usefully employed in addicts is to give 0.8-1.2 mg naloxone
     intramuscularly before awakening the patient with an intravenous
    naloxone dose of 0.4-0.8 mg (higher doses are rarely needed) (personal
    communication by D. Jacobsen, 1991).  This has been shown to be a
    useful practical approach, since many addicts leave the hospital
    immediately following the effect of the intravenous dose.  Since
    naloxone has a shorter duration of action than the opiate, patients
    are commonly readmitted within one hour with miosis, coma and impaired
    respiration.  This approach to treatment, however, requires adequate
    ventilatary support for the patient because of the short delay before
    the intravenous dose is given.

         Naloxone may also be given as a continuous intravenous infusion
    (about 0.5 mg/h in isotonic saline) to counteract effects of morphine
    metabolites in patients with acute renal failure (Bodd et al., 1990).

    2.12.3  Other consequential or supportive therapy

         Since many of these patients suffer from impaired respiration or
    respiratory arrest, it is extremely important to give oxygen and to
    support ventilation immediately while waiting for naloxone to be
    available for injection. If ventilation is under control and cyanosis
    is regressing, one should consider giving an intramuscular dose of
    naloxone  before the intravenous dose (see section 2.12.2).

         Pulmonary congestion or oedema is occasionally seen in opioid
    (heroin) poisoning. It is usually transient and responds to supportive
    therapy (oxygen and ventilation support) and naloxone.

    2.12.4  Areas where there is insufficient information to make

         There are anecdotal reports of beneficial effect of naloxone in
    other types of acute poisoning, e.g., with ethanol or clonidine. In
    the case of ethanol, these results have not been confirmed in well-
    controlled studies on volunteers or in intoxicated patients (Nuotto et
    al., 1984). The claimed effect in clonidine poisoning has also been
    challenged (Wiley et al., 1990).  There are insufficient data to
    recommend the use of naloxone in poisonings other than those involving

    2.12.5  Proposals for further studies

         Studies of the effect of naloxone in other acute poisonings
    should be encouraged. It could, however, be argued that enough studies
    have been performed on the use of naloxone in ethanol intoxication to
    rule out a possible beneficial effect. On the other hand, there is
    certainly a lack of controlled studies on the possible effect of
    naloxone in clonidine poisoning.

         If effects of naloxone are observed in patients assumed to have
    been poisoned by non-opioids, urine specimens should be collected and
    analysed by RIA for presence of opioids.  Otherwise such "case
    reports" are of little value.

    2.12.6  Adverse effects

         Naloxone possesses a high therapeutic index, but it may provoke
    withdrawal signs and symptoms, e.g., seizures, in (heroin) addicts.
    Other adverse reactions, as described below, are very rarely seen.

         Cardiac arrhythmias and, in particular, ventricular fibrillation
    have resulted from rapid reversal of opiate effects with naloxone. 
    Such events may be a particular problem in patients who have recently
    undergone surgery or those habituated to opiates (Cuss et al., 1984). 
    These reactions may result from a release of sympathetic transmitters,
    since a rise in blood pressure and tachycardia have also been

         Some cases of pulmonary oedema following naloxone use in
    anaesthetic practice have been reported, but it is unclear in this
    situation which is the responsible agent: the anaesthetic, the opiate
    or the antagonist (Partridge & Ward, 1986).

    2.12.7  Restrictions of use

         The fear of provoking withdrawal signs and symptoms should not
    hinder use of naloxone in those who need it clinically.

    2.13 Model Information Sheet

    2.13.1 Uses

         Naloxone is indicated in the management of opiate poisoning, both
    definite and suspected. Opiate poisoning should be considered in
    comatose patients with impaired respiration. Miosis is an unreliable
    sign and is not required for a diagnosis of opioid poisoning.  The
    high wide therapeutic index of naloxone allows its use when a
    diagnosis of opioid poisoning is uncertain.

    2.13.2  Dosage and route

         Since naloxone is a competitive antagonist of opiate poisoning,
    there can be no absolute guidelines on dosage.  Naloxone should be
    given intravenously, in successive doses of 0.4 to 2.0 mg, until the
    desired response has been obtained.  It should be noted that to
    reverse the effects of partial agonists/antagonists, e.g.,
    pentazocine, buprenorphine and dextropropoxyphene, much larger doses
    may be required, and it may prove impossible to reverse the effects of

         Failure to respond to a total dose of 10 mg usually indicates: a)
    that poisoning is not due to opiates; b) that poisoning is due to a
    partial agonist/antagonist; or c) that hypoxic brain damage has
    occurred. It should be noted that dextropropoxyphene has been reported
    to produce cardiac toxicity that is  not reversible by naloxone

         The duration of action of naloxone is short; careful monitoring
    is required and repeated doses may be necessary.  The alternative is
    an intravenous infusion of naloxone.  The use of an hourly infusion of
    two-thirds of the dose of naloxone required to resuscitate the patient
    has been reported to be effective, but dosage should be always
    titrated to the individual patient.

         Another alternative, which may be appropriate for opiate addicts,
    is to give naloxone (0.8-1.2 mg)  intramuscularly before waking the
    patient with an intravenous dose of 0.4-0.8 mg.  However, adequate
    ventilatory support must be given.  The patient then has a "depot" of
    antidote in case he/she departs soon after the initial treatment (as
    many addicts do).

         The dose given to  children should be reduced according to body
    weight (0.01 mg/kg initially).

    2.13.3  Precautions/contraindications

         Naloxone may induce symptoms and signs of acute opiate withdrawal
    in addicts. If seizures occur they are best controlled with diazepam
    (10-30 mg, intravenously).  No dosage alterations seem necessary in

    the case of changes in renal function.  The dose in children should be
    adjusted on a body-weight basis to that used in adults.

         Appropriate protective precautions need to be taken by hospital
    staff in the case of opiate addicts, bearing in mind the risk of
    infection from blood-borne diseases such as hepatitis B and human
    immunodeficiency virus (HIV).

    2.13.4  Adverse effects

         Naloxone has a very high therapeutic index and adverse effects
    are rarely seen. Ventricular arrhythmias including ventricular
    fibrillation have been reported following rapid reversal of severe
    opiate intoxication. This may be avoided if oxygen and adequate
    ventilatory support are also given.  The management of withdrawal
    symptoms in addicts is discussed in section 2.13.3.

    2.13.5 Use in pregnancy and lactation

         Naloxone is not teratogenic in animals, but no relevant human
    data exist.  Naloxone treatment does not appear to be a
    contraindication to breast feeding, although the opiate poisoning
    being treated may itself be a contraindication.

    2.13.6  Storage

         Naloxone for injection should be stored protected from light. 
    Its shelf-life is 3 years.

    2.14  References

    Aitkenhead AR, Derbyshire DR, Pinnock CA, Achola K, & Smith G  (1984) 
    Pharmacokinetics of intravenous naloxone in healthy volunteers. 
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    Asali LA  (1983)  Determination of naloxone in blood by high
    performance liquid chromatography. J Chromatogr, 278: 329-335.

    Asali LA & Brown KF (1984)  Naloxone protein binding in adult and
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    Badawy AA-R, Evans M, Punjani NF, & Morgan CJ (1983)  Does naloxone
    always act as an opiate antagonist?  Life Sci, 33(Suppl 1): 739-742.

    Banner W, Lund ME, & Clawson L (1983)  Failure of naloxone to reverse
    clonidine toxic effect. Am J Dis Child, 137: 1170-1171.

    Barraclough CJ & Lowe RA (1982)  Failure of naloxone to reverse the
    cardiotoxicity of Distalgesic overdose. Postgrad Med J, 58: 667-668.

    Bell EF (1975)  The use of naloxone in the treatment of diazepam
    poisoning.  J Paediatr, 87: 803-804.

    Berkowitz BA, Ngai SH, Hempstead J, & Spector S (1975) Disposition of
    naloxone: Use of a new radio-immunoassay.  J Pharm Exp Ther, 195(2):

    Berkowitz BA (1976)  The relationship of pharmacokinetics to
    pharmacological activity: Morphine, methadone and naloxone.  Clin
    Pharmacokinet, 1: 219-230.

    Blumberg H, Wernick T, Dayton HB, Hansen RE, & Rapaport DN  (1966) 
    Toxicological studies on the narcotic antagonist naloxone.  Toxicol
    Appl Pharmacol, 8: 335.

    Bodd E, Jacobsen D, Lund E, Ripel A, Morland J, & Wiik-Larsen E 
    (1990) Morphine-6-glucuronide might mediate the prolonged opioid
    effect of morphine in acute renal failure. Hum Exp Toxicol, 9:

    Bradberry JC & Raebel MA (1981)  Continuous infusion of naloxone in
    the treatment of narcotic overdose.  Drug Intell Clin Pharm, 15:

    Buchner LH, Cimino JA, Raybin HW, & Stewart B (1972)  Naloxone
    reversal of methadone poisoning.  NY State J Med, 72: 2305-2309.

    Christensen KN & Huttel M (1979)  Naloxone does not antagonise
    diazepam-induced sedation.  Anaesthesiology, 51: 187.

    Cohen MR, Cohen RM, Pickar D, Weingartner H, & Murphy DL  (1983)  High
    dose naloxone infusions in normals.  Dose-dependent behavioural,
    hormonal and physiological responses.  Arch Gen Psychiatry, 40:

    Cuss FM, Colaço CB, & Baron JH (1984)  Cardiac arrest after reversal
    of effects of opiates with naloxone. Br Med J, 288: 363-364.

    Dingledine R, Inversen LL, & Breuker E (1978)  Naloxone as a GABA
    antagonist: evidence from iontophoretic, receptor binding and
    convulsant studies.  Eur J Pharmacol, 47: 19-27.

    Drummond GB, Davie IT, & Scott DB (1977)  Naloxone: dose-dependent
    antagonism of respiratory depression by fentanyl in anaesthetised
    patients.  Br J Anaesth, 49: 151-154.

    Evans LEJ, Roscoe P, Swainson CP, & Prescott LF (1973)  Treatment of
    drug overdose with naloxone, a specific narcotic antagonist.  Lancet,
    1: 452.

    Fishman J, Roffwarg H, & Hellman, L. (1973)  Disposition of naloxone
    - 7,8,3H in normal and narcotic-dependent men.  J Pharmacol Exp Ther,
    187: 575-580.

    Fishman J, Hahn EF, & Norton BI (1975)  Comparative in vivo
    distribution of opiate agonists and antagonists by means of double
    isotope techniques. Life Sci, 17: 1119-1126.

    Fujimoto JM (1969)  Isolation of two different glucuronide metabolites
    of naloxone from the urine of rabbit and chicken.  J Pharmacol Exp
    Ther, 168: 180-186.

    Fujimoto JM, Roerig S, Wang RIH, Chatterjie N, & Intrirrisi CE (1975) 
    Narcotic antagonist activity of several metabolites of naloxone and
    naltrexone tested in morphine dependent mice (38558).  Proc Soc Exp
    Biol Med, 148: 443-448.

    Gober AE, Kearns GL, Yorkel RA, & Danziger L (1979)  Repeated naloxone
    administration for morphine overdose in a 1 month old infant.
    Paediatrics, 63: 606-608.

    Gold MS, Pottash AC, Sweeney DR, & Kleber HD (1980) Opiate withdrawal
    using clonidine. A safe, effective, and rapid nonopiate treatment. J
    Am Med Assoc, 243: 343-346.

    Goldfrank L, Weisman RS, Errick JK, & Lo MW (1986)  A dosing nomogram
    for continuous infusion intravenous naloxone.  Ann Emergency Med, 15:

    Gourlay GK & Coulthard K (1983)  The role of naloxone infusions in the
    treatment of overdoses of long half-life narcotic agonists.
    Application to nor-methadone.  Br. J Clin Pharmacol., 15: 269-271.

    Handal KA, Schauben JL, & Salamone FR (1983)  Naloxone.  Ann Intern
    Med, 12: 438-445.

    Hahn EF, Lahita R, Kreek J, Duma C, & Intrurrisi CE (1983)  Naloxone
    radio-immunoassay: an improved antiserum.  J Pharm Pharmacol, 35:

    Hassan MMA, Mohammed ME, & Mian MS (1985)  Naloxone hydrochloride. 
    Anal Profiles Drug Subst, 14: 453-489.

    Hatano S, Keane DM, Wade MA, & Sadove MS (1975)  Naloxone reversal for
    anaesthetic dosages of pentazocine. Anaesth Rev, 2: 11-15.

    Henry J & Volans G (1984)  ABC of Poisoning: Analgesics: Opioids.  Br
    Med J, 289: 990-993.

    Jasinski DR, Martin WR, & Haertzen CA (1967)  The human pharmacology
    and abuse potential of N-allyl noroxymorphone (naloxone).  J Pharm Exp
    Ther, 157: 420-426.

    Jeffcoate WJ, Herbert M, Cullen MH, Hastings AG, & Walder CP (1979) 
    Prevention of effects of alcohol intoxication by naloxone. Lancet, 2:

    Jefferys DB, Flanagan RJ, & Volans GN (1980)  Reversal of ethanol-
    induced coma with naloxone.  Lancet, 1: 308-309.

    Johnstone RE, Jobes DR, Kennell EM, Behar MG, & Smith TC (1974) 
    Reversal of morphine anaesthesia with naloxone.  Anaesthesiology, 41:

    Jordan C (1980)  Respiratory depression following diazepam: reversal
    with high-dose naloxone.  Anaesthesiology, 53: 293-298.

    Kaufman RD, Gabathuler ML, & Bellville JW (1981)  Potency, duration of
    action and pA2 in man of intravenous naloxone  measured by reversal of
    morphine-depressed respiration.  J Pharmacol Exp Ther, 219: 156-162.

    Kaufman JJ, Semo NM, & Koski WS (1975)  Microelectrometric titration
    measurements of the pKa's and partition and drug distribution
    coefficients of narcotics and narcotic antagonists and their pH and
    temperature dependence.  J Med Chem, 18: 647-655.

    Kotlinska J & Langwinski R (1990) The lack of effect of opioid
    agonists and antagonists on some acute effects of ethanol. Pol J
    Pharmacol Pharm, 42: 129-135.

    Kulig K, Duffy J, & Rumack BH (1982) Naloxone for treatment of
    clonidine overdose. J Am Med Assoc, 247: 1697.

    Longnecker DD, Grazis PA, & Eggors WWN (1973)  Naloxone for antagonism
    of morphine-induced respiratory depression.  Anaesth Analg, 53:

    McNicholas LF & Martin WR (1984)  New and experimental therapeutic
    roles for naloxone and related opioid antagonists.  Drugs, 27: 98-93.

    Martin WR (1976)  Naloxone. Ann Intern Med, 85: 765-768.

    Martindale (1982) In: Reznolds JEF ed.  The extra pharmacopoeia, 28th
    ed.  London, Pharmaceutical Press.

    Meffin PF & Smith KJ (1980)  Gas chromatographic analysis of naloxone
    in biological fluids. J Chromatogr, 183: 352-356.

    Misra AL (1978)  Metabolism of opiates.  In: Factors affecting the
    action of narcotics.  New York, Raven Press, pp 297-343.

    Ngai SH, Berkowitz BA, Yang JC, Hampstead J, & Spector S (1976) 
    Pharmacokinetics of naloxone in rats and in man: Basis for its potency
    and short duration of action.  Anaesthesiology, 44: 398-401.

    North DS, Wieland MJ, & Peterson CD (1981) Naloxone administration in
    clonidine overdosage. Ann Emergency Med, 10: 397.

    Nuotto E, Palva ES, & Seppala T (1984) Naloxone-ethanol interaction in
    experimental and clinical situations. Acta Pharmacol Toxicol, 54:

    Pace NL, Parrish RG, Lieberman MM, Wong KC, & Blatnick RA (1979) 
    Pharmacokinetics of naloxone and naltrexone in the dog.  J Pharmacol
    Exp Ther, 208: 254-256.

    Partridge BL & Ward CF (1986)  Pulmonary edema following low-dose
    naloxone administration. Anesthesiology, 65: 709-710.

    Sawynok J, Pinsky C, & Labella FS (1979)  Mini review on the
    specificity of naloxone as an opiate antagonist.  Life Sci, 25:

    Smits SE & Takemori AE (1970)  Quantitative studies on the antagonism
    by naloxone of some narcotic and narcotic-antagonist analgesics.  Br
    J Pharmacol, 39: 627-638.

    Social Welfare Board (1976)  Nalone (naloxon). Uppsala, Sweden, Social
    Welfare Board, Pharmaceuticals Department, pp 7-9.

    Stile IL, Fort M, Marotta F, Wurzburger R, Hiatt IM, & Hegyi T (1984) 
    Pharmacokinetics of naloxone in premature infants.  Paediatr Res,
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    Tenenbein M (1984)  Continuous naloxone infusion for opiate poisoning
    in infancy.  J Pediatr, 105: 645-647.

    Terry MD, Hisayasu GH, Kern JW, & Cohen JL (1984)  High performance
    liquid chromatographic analysis of naloxone in human serum.  J
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    United States Pharmacopeial Convention, Inc.

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    Metabolites of naloxone in human urine.  J Pharm Sci, 60: 1567-1568.

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    poisoning in young children. J Pediatr, 116: 654-658.

    Windholz M ed.  (1983)  The Merck index: An encyclopedia of chemicals,
    drugs and biologicals, 10th ed.  Rahway, New Jersey, Merck and Co,


    3.1 Introduction

         Acute poisoning is currently one of the main causes of hospital
    admission in developed countries.  Benzodiazepines (BZDs) are the most
    commonly used drugs throughout the world and their abuse may be
    responsible for the impairment of memory and for dependence.  An acute
    overdose can result in long-lasting coma, which is generally treated
    with supportive measures. Flumazenil, an imidazobenzo-diazepine
    (AnexateTM), has been shown to reverse the sedative, anti-
    convulsant, and muscle-relaxant effects of BDZs.  It has no convulsive
    action in itself and its use has therefore been proposed to counteract
    benzodiazepine action in anaesthetics, clinical toxicology and
    intensive care.

    3.2  Name and Chemical Formula of Antidote

    *    Flumazenil AnexateR (Roche Laboratories)
    *    Ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]
    *    Empirical formula: C15H14O3N3F
    *    Relative molecular mass: 303.3
    *    Therapeutic class : Imidazobenzodiazepine
    *    CAS number: 78 755-81-4
    *    Conversions:1 mmol   =    303.3 mg
                     1 g      =    3.3 mmol
                     µmol/l   =    3.3 x µg/ml
                     µg/ml    =    0.3 x µmol/l

    3.3  Physico-chemical Properties

         Physico-chemical properties of flumazenil are given in Table 1.

         Flumazenil remains stable when exposed to light and when stored
    for 2 years at 35° C.  The loss of weight on drying is up to 1%.

    3.4  Pharmaceutical Formulation and Synthesis

         No information is available on the routes of synthesis and

         Flumazenil is supplied for parenteral administration in vials
    containing 5 or 10 ml aqueous solution (0.1 mg/ml).  It is available
    for oral administration as tablets of 10, 20 or 30 mg.

    Table 1.  Physico-chemical properties of flumazenila


    Melting point                                      198-202 °C

    Solubility in water                                   < 1 g/l

    Solubility in organic solvents (g/l)
        chloroform                                          < 250
        methanol                                            <  17
        ethyl acetate                                       <   3
        diethyl ether                                       <   1

    Solubility at various pH values (g/l)
        (in aqueous buffered solution at 37° C)
        pH 1.2                                                  3
        pH 5.3                                                0.7
        pH 7.5                                                0.6

    Acidity (10% aqueous solution)                        4.5-7.5

    pKa (in weak base)                                        1.7

    a  Personal communication from Roche Laboratories (1988)

    3.5  Analytical Methods

    3.5.1  Identification of the antidote

         Information on the identification of flumazenil was provided by
    Roche Laboratories (personal communication, 1988).  Infrared spectroscopy

         The infrared spectrum (625-4000 cm-1) of a sample (a 1:300
    solid dispersion in potassium bromide) is compared qualitatively with
    that of a reference substance.  Ultraviolet absorption

         A portion (85-95 mg) of the sample is dissolved in approximately
    100 ml of ethanol and diluted to 150 ml with ethanol (solution 1). 
    This solution is then diluted ten-fold with ethanol to give solution
    2, which is further diluted ten-fold with ethanol to give solution 3.
    The position and absorbance of solution 3 is measured
    spectrophotometrically at the maximum (245 nm) and minimum (228 nm)
    wavelengths, against ethanol, in quartz cells.  Thin-layer chromatography

         The TLC details are as follows:

         *     layer:  Silica gel 60 F254

         *     mobile phase:  Chloroform/ethanol (90/10 v/v)

         *     sample solution: 10 ml of the ampoule solution is extracted
               with 1 ml of chloroform

         *     standard solution: 5 mg of flumazenil is dissolved in 5 ml
               of chloroform saturated with water

         *     front distance: 12 cm

         *     migration time approx: 30 min

         *     detection: the plate is dried in a current of warm air for
               5 min, and examined under shortwave light.  Decreasing
               fluorescence due to flumazenil occurs at 254 nm
               (ultraviolet region). When the plate is sprayed with
               Dragendorff's reagent, flumazenil appears as an orange
               spot.  The Rf value is approximately 0.5.

    3.5.2  Quantification of the antidote in biological samples

         The determination of flumazenil in plasma by gas-liquid
    chromatography (GLC) with nitrogen phosphorus detection is a sensitive
    and specific method, the detection limit being 3 ng/ml (Abernethy et
    al., 1983).  An ethyl acetate extraction (neutral pH) of 0.1-3 ml
    plasma is used for sample preparation.  When methylclonazepam is used
    as an internal standard, the graph is linear for plasma concentrations
    up to 200 ng/ml.  The retention time for flumazenil is 3.96 min.

         High-performance liquid chromatography (HPLC) with UV detection
    at 254 nm is a sensitive method for determination in urine or plasma,
    the detection limit being about 10 ng/ml (Timm & Zell, 1983; Bun et
    al., 1989).  When the  n-propyl ester analogue is used as an internal
    standard, the graph is linear for plasma concentrations up to 320

    3.5.3  Analysis of the toxic agent in biological samples

         Three major methods for the quantitative analysis of BZDs in
    plasma or serum are used:

    *    HPLC with UV detection at 246 nm (detection limits are 5-50 µg/ml
         of serum) (Rocher, 1984);

    *    immunoenzymology by the EMIT method for a semiquantitative
         determination (metabolites also measured) of diazepam levels,
         completed by a chromatographic method (sensitivity from 0.3 to 2
         µg/ml) (Rocher, 1984);

    *    gas-liquid chromatography (Pellerin, 1986).

    3.6  Shelf-life

         Vials ready for use are stable at room temperature (15-25° C) for
    three years.

    3.7  General Properties

         Flumazenil has been shown to block all the typical BZD effects
    (anticonvulsive, sedative, anxiolytic, muscle relaxant, and amnesic). 
    It acts as a potent BZD-specific antagonist by competing at the
    central synaptic gamma-aminobutyric acid (GABA) receptor sites in a
    dose-dependent manner, but does not seem to antagonise BZD effects at
    peripheral GABA-ergic (renal, cardiac, etc.) receptor sites (Mohler et
    al., 1981).  It possesses agonist properties and has a specific, but
    discreet, anticonvulsive effect without inducing drowsiness or muscle
    relaxation (Abernethy et al., 1983; Timm & Zell, 1983; Haaefely, 1983;
    Rocher, 1984; Scollo-Lavizzari, 1984; personal communication by Roche
    Laboratories, 1988).  In addition, it antagonizes the sedative effects
    of other compounds that act through GABA receptors, such as zopiclone
    (Mohler et al., 1981).

    3.8  Animal Studiesc

    3.8.1  Pharmacodynamics

         Flumazenil has been tested for its ability to induce withdrawal
    signs in animals pretreated with benzodiazepine; the signs included
    emesis, tremors, rigidity and clonic convulsions.


    c  Personal communication by Roche Laboratories to the IPCS, 1988

         Rats that had been pretreated with an oral dose (10 or 100 mg/kg)
    of diazepam for 12 days were administered flumazenil (10 mg/kg)
    intravenously.  Signs were very mild even at 100 mg/kg.

         Cats were pretreated intraperitoneally for 16 days with either a
    10-mg/kg dose of lorazepam twice daily or a 1-mg/kg dose of triazolam
    once daily. Flumazenil (100 mg/kg) was then administered
    intraperitoneally either immediately or 1.5, 6, 12, 48, and 60 h after
    the last dose.  Symptoms such as rigidity, vocalization and tachypnoea
    lasted 30 min, whereas others such as hypersalivation lasted 2 h.

         Flumazenil (1 to 15 mg/kg) was administered intragastrically to
    rats that had been pretreated with daily diazepam doses of 113 mg/kg
    for about 6 months. Abstinence syndromes increased with increasing
    dose of flumazenil and reached a plateau.

         The intragastric administration of flumazenil (15 mg/kg per day)
    to cats pretreated with flurazepam (5 mg/kg per day) for 35 days led
    to withdrawal symptoms (increasing muscle tone, tremors, piloerection,
    mydriasis, and hypersalivation) 24 h after the last dose of
    flurazepam.  No convulsions were observed.

         Intramuscular administration of flumazenil (5 mg/kg) to squirrel
    monkeys and baboons, pretreated with oral doses of lorazepam,
    triazolam (3 mg/kg per day), oxazepam (40 or 80 mg/kg per day) or
    diazepam (8-20 mg/kg per day), produced withdrawal signs.  However, no
    withdrawal signs were precipitated by flumazenil in monkeys treated
    with oral midazolam (30 mg/kg) or in barbital-dependent rhesus monkeys
    (the length of pretreatment with BZD was not specified).

         The severity of withdrawal signs resulting from the blocking of
    BZD receptors by flumazenil depends on the species tested, the dose of
    BDZ used to develop physiological dependence, and the duration of

    3.8.2  Pharmacokinetics  Absorption

         A single dose of flumazenil (125 mg/kg) in a carboxymethyl
    cellulose suspension produced a maximum plasma concentration in rats
    of 9.9 µg/ml after 20 min.  The bioavailability was 0.55.  In rabbits,
    the maximum concentration 90 min after a single dose of flumazenil
    (150 mg/kg) was 15 µg/ml.  The bioavailability was 0.60.  Distribution

         When total radioactivity was measured in rats 0.5, 7, 24, 96, and
    192 h after an intravenous dose of 14C-labelled flumazenil (2
    mg/kg), the highest level was found at 0.5 h in the kidney, liver and

    intestine.  None was found at 192 h.  The volume of distribution
    ranged from 0.71 to 1.87 l/kg.  Elimination

         Studies on rats given an oral dose (50 mg/kg) of 14C-labelled
    flumazenil and on dogs given an intravenous dose of 4 mg/kg showed
    three main inactive metabolites:

    *    Ro 15-3890 acid and major metabolite (72% in the rat, 30-60% in
         the dog);

    *    Ro 15-4965 hydroxyethyl derivative (3% in the rat);

    *    Ro 15-6877  N-demethyl derivative (1% in the rat, 1-13% in the

         Table 2 presents elimination data in three different species.  In
    these species, 90% of the intravenously or orally administered
    flumazenil was eliminated, mainly as metabolites, within 48 h.  One
    third was eliminated in the faeces and two-thirds in the urine.

    Table 2.  Elimination of flumazenil in the rat, rabbit and dog


    Species     Dose           Total plasma          T´
                                clearance           (min)
                             (ml/min per kg)

    Rat         2 mg/kg            114                7.4

    Rabbit      0.5 mg/kg           24               34

    Dog         5 mg                21               48

    3.8.3  Toxicology  Acute toxicity

    a)   Intravenous administration to rats and mice

         An aqueous solution of 0.1 mg flumazenil/ml was used and was
    administered at a dose of 2.5 mg/kg to mice and 1 mg/kg to rats.  No
    abnormal clinical signs and no deaths occurred.  LD50 values were
    not determined; these doses (50 to 250 times higher than the clinical
    doses) were well tolerated in the two species.

         A flumazenil solution with a concentration of 50 mg/ml was
    subsequently used and the LD50 values given in Table 3 were obtained
    (95% confidence intervals).  Deaths occurred 30 min after the
    injection, preceded by rigidity and clonic convulsions.

    Table 3.  Intravenous LD50 values (mg/kg) for the mouse and rat


    Species         Male            Female

    Mouse          143-198          145-175

    Rat             85-167          112-231

    b)   Intravenous administration to the dog

         The administration of daily doses of 0.01 to 0.03 mg/kg was well
    tolerated and no deaths were observed.  LD50 values were not
    determined; the doses (15 to 30 times higher than the clinical doses)
    were again well tolerated.

    c)   LD50 values (mg/kg) for the rat, mouse and rabbit

         When flumazenil was administered orally to rats, mice and rabbits
    (Table 4), deaths were observed within three days, associated with
    decreased motor activity, catatonic state and tremors.

    Table 4.  LD50 values (mg/kg) for the rat, mouse and rabbit


    Species           Male             Female

    Mouse             2500             1300

    Rat               4200             4200

    Rabbit            2000             2000
                                                Subacute toxicity

         Systemic tolerance was good in both rats and dogs administered
    flumazenil intravenously at dosages up to 10 mg/kg per day for 4
    weeks.  Chronic toxicity

         In 13-week studies using an oral aqueous solution of flumazenil,
    very good tolerance was shown by rats at dosages of 0.5, 25 and 125
    mg/kg per day and by dogs at 0.5, 20, and 80 mg/kg per day.  No
    haematological, biochemical or gross pathological abnormalities were
    observed.  Embryotoxicity

         Studies on rats (between the 7th and 16th day of gestation) and
    rabbits (between the 7th and 19th day of gestation) revealed no signs
    of embryotoxicity at dosages of 15, 50, and 150 mg/kg per day.  Mutagenicity

         Flumazenil was not mutagenic in the Ames test or micronucleus
    test, or in tests using  Saccharomyces cerevisiae or Chinese hamster
    V79 cells.

    3.9  Volunteer Studies

    3.9.1  Pharmacodynamics  BZD antagonist effect

         Efficacy studies were performed on 125 healthy volunteers with
    oral doses of flumazenil up to 20 mg, the aim being to antagonize the
    effects of diazepam, flunitrazepam and midazolam on the CNS (Darragh,
    1981; Lupolover, 1983).  These studies demonstrated the antagonist
    effect of flumazenil, which rapidly abolished the hypnotic-sedative
    BZD effects.  Other studies used meclonazepam (Darragh et al., 1981),
    diazepam (Darragh et al., 1982), flunitrazepam (Gaillard & Blois,
    1983) and midazolam (Forster et al., 1983).  In studies by Ziegler &
    Schalch (1983) and Lauven et al. (1985), flumazenil was administered
    to subjects during continuous midazolam infusion after the attainment
    of a pharmacokinetic and pharmacodynamic steady state, at which point
    subjects were deeply asleep.  The degree and duration of the effect of
    flumazenil depended on the BZD dose, the antagonist dose and the time
    that had elapsed since the BZD was given.  In the study by Ziegler &
    Schalch (1983), baseline levels of vigilance and orientation were
    reached within 1 min.  Lauven et al. (1985) used higher midazolam and
    flumazenil dosages and his patients awoke within 28 to 48 seconds.  No
    signs of BZD withdrawal effects were seen in short-term studies (one
    single dose) on healthy volunteers given flumazenil to antagonize BZDs
    (Amrein, 1987).

         The efficacy of flumazenil in antagonizing the effects of
    midazolam was also clearly demonstrated in the double-blind placebo-
    controlled study by Rouiller et al. (1987).  Intrinsic effects

         Most studies on healthy human volunteers have shown little or no
    intrinsic effect of flumazenil when administered alone.  The mild
    sedation reported by Amrein (1987) occurred after the administration
    of oral doses greater than 100 mg.

         Scollo-Lavizzari (1984) observed some anticonvulsant effects in
    epileptic patients.  Decreased amplitude of auditory evoked potentials
    has also been described (Laurian et al., 1984; Schoepf et al., 1984). 
    Mild, nonspecific effects such as increased alertness may occur after
    the administration of doses very much higher than those used
    clinically (Laurian et al., 1987).

    3.9.2  Pharmacokinetics  Absorption

         Following oral administration of a 200-mg dose of flumazenil, the
    highest plasma concentration (Cmax) ranged from 147 to 349 µg/l and
    was reached within 20 to 45 min.  The mean bioavailability of the
    tablets used was about 17% and the inter-individual variability was
    7-29% (Pellerin, 1986).  Distribution

         The proportion of flumazenil bound to plasma proteins is 50%
    (two-thirds of which is bound to albumin).  Values for the mean
    steady-state volume of distribution of 0.95 l/kg (personal
    communication by Roche Laboratories, 1988) and 1.23 l/kg (Roncari et
    al., 1986) have been determined.  Elimination

         Ninety-nine per cent of the flumazenil administered is
    metabolized by the liver, and 1% is excreted unchanged in the urine. 
    Mean total blood clearance, for which values of 59 l/h (Pellerin,
    1986) and 72 l/h (Roncari et al., 1986) have been determined, is
    essentially due to the hepatic clearance.  The apparent plasma half-
    life in healthy volunteers has been reported to be 53-58 min (Roncari
    et al., 1986; personal communication by Roche Laboratories, 1988).

    3.9.3  Tolerance of flumazenil

         In the study by Rouiller et al. (1987), no objective agonist
    effects or biological toxicity of flumazenil could be demonstrated in
    six healthy volunteers.

    3.9.4  Other studies

         There is evidence that central nervous system effects of ethanol
    are mediated through the GABA system.  For this reason, the effect of
    flumazenil on psychometric performance was studied in eight healthy
    volunteers with stable blood ethanol levels of 1.6 g/l (35 mmol/l)
    under a placebo-controlled double-blind design (Clausen et al., 1990). 
    Flumazenil did not improve psychomotor functions in these ethanol-
    intoxicated subjects, which is in agreement with experience in
    clinical toxicology.

    3.10  Clinical Studies - Clinical Trials

         Flumazenil was first used clinically in patients with iatrogenic
    benzodiazepine overdose due to mechanical ventilation or status
    epilepticus (Scollo-Lavizzari, 1983).

         Clinical studies can be grouped under the headings
    anaesthesiology and toxicology (Amrein, 1986).

    3.10.1 Anaesthesiology  General anaesthesia

         Three placebo-controlled studies have been conducted in patients
    who were given flunitrazepam for general anaesthesia.

         Jensen et al. (1985) reported that a 0.3-mg to 0.7-mg dose of
    flumazenil awoke all patients within 5 min, compared with only 35% of
    the patients in the placebo-treated group (P < 0.001 for sedation,
    orientation and amnesia).

         In a study of 60 patients, Tolksdorf et al. (1986) found that
    patients treated with flumazenil were less sedated than placebo-
    treated patients (P < 0.05) following flunitrazepam sedation (from 5
    min to 1 h after the administration of flumazenil), better orientated
    at 15 min, and less amnesic.  Ellmauer et al. (1986) reported similar
    results in 57 patients given a 0.1- to 1-mg dose of flunitrazepam (P
    < 0.005).

         No significant difference was observed after 2 h between the
    placebo-treated and flumazenil-treated patients in any of the three
    studies described in this section.

         Midazolam effects were reversed by flumazenil in an open study
    including 18 intracranial surgery patients (Chiolero et al., 1988). sedation

         In a 74-patient open study (Geller et al., 1986) and a 40-patient
    placebo-controlled study (Knudsen et al., 1986), in which either
    midazolam or diazepam was used, there was a significant difference
    between flumazenil- and placebo-treated patients.  In the former
    study, patients were awakened by a 0.1- to 0.6-mg dose of flumazenil
    within 1 to 2 min.  In the study by Knudsen et al. (1986), 80% of the
    flumazenil-treated patients were awake 5 min after receiving the dose
    compared with 50% in the placebo group (P < 0.05).

    3.10.2  Benzodiazepine overdose or intoxication

         Three different studies have indicated that flumazenil may be an
    effective tool for the management of intoxication (either intentional
    or iatrogenic) with BZD in the presence or absence of other agents. 
    Owing to its safety and specificity, flumazenil could be used in the
    initial treatment of poisoning and coma of unknown origin.  In a study
    by Hofer & Scollo-Lavizzari (1985) based on 13 patients, a 1.5-to 10-
    mg dose of flumazenil administered intravenously at a rate of 1.5 to
    2.5 mg/min reversed the CNS depression induced by various BZDs within
    1 to 2 min.

         Geller et al. (1985) treated 34 patients (23 cases of intentional
    drug intoxication and 11 of iatrogenic BZD overdose) by means of
    intravenous injections of 0.1 mg flumazenil every 30 seconds until the
    patient regained consciousness.  The treatment proved to be extremely
    effective, providing reversal effects lasting up to 2 h.

         Bismuth et al. (1985) treated patients for BZD overdose in a
    double-blind randomized study, injecting a single dose of either
    flumazenil or placebo.  Two of the 20 placebo patients awoke
    partially, compared with 17 of the 20 flumazenil-treated patients (one
    experienced seizures interrupting the study).  In a second open study
    (Bismuth et al., 1986) based on 37 patients, 6 showed no response to
    doses of flumazenil ranging from 5 to 9.5 mg (mixed intoxication), 11
    showed partial awakening (no possible written response) at a dose of
    2.1 ± 1.6 mg (mixed intoxication), and 20 were completely awakened by
    a dose of 1.4 ± 0.7 mg.  The awakening was only temporary and return
    to coma occurred after an interval of 15 min to 5 h.  Permanent
    recovery occurred in a patient suffering intoxication due to
    triazolam, a BZD with a short half-life, after a single administration
    of flumazenil.

         More recent placebo-controlled double-blind studies have
    confirmed the beneficial effect of flumazenil in cases of BZD
    poisoning (Aarseth et al., 1988; Ritz et al., 1990).

    3.11  Clinical Studies - Case Reports

         The many controlled clinical studies of the effect of flumazenil
    limit the need for information from case reports.  In the clinical
    studies reported, there have been few adverse effects associated with

    the use of flumazenil.  There have, however, been case reports of
    seizures followed by ventricular tachycardia associated with the use
    of flumazenil in combined poisonings with cyclic antidepressants and
    BZD (Bismuth et al., 1985).

         In one report, death was claimed to have been associated with
    flumazenil administration in an old, obese and anaemic woman who had
    been sedated with midazolam (4 mg, intravenous) prior to gastroscopy
    (Lim, 1989).  During the investigation she suffered cardiac arrest;
    flumazenil was given promptly and she recovered temporarily, but then
    gradually deteriorated and died 16 h later. According to Birch &
    Miller (1990), the death of this patient was probably not related to
    flumazenil administration.

         Recently, successful treatment was achieved by administering
    flumazenil as an intravenous bolus (0.02 mg/kg) and then as a
    maintenance dose of 0.05 mg/kg per h to a newborn baby with recurrent
    apnoea due to BZDs taken by his mother (Richard et al., 1991).

         The benefit from the diagnostic use of flumazenil in coma of
    unknown origin has been reported in two recent cases (Burkhart &
    Kulig, 1990).  When flumazenil is used with caution in such
    situations, time may be saved and further expensive diagnostic
    procedures, e.g., cerebral computerized tomographic (CT) scan,

    3.12  Summary of Evaluation

         Flumazenil appears to be a antagonist to BZDs and other GABA-
    ergic agents.  This antagonism, following intravenous injection, has
    been reported to be sensitive in cases of intoxication resulting
    solely from BZDs (the reversal of BZD effects being observed with
    doses of less than 2 mg), rapid in onset (within 2 min), and short-
    lived (effects last for less than 30 min).

    3.12.1  Indications

         In controlled clinical trials, flumazenil significantly
    antagonizes BZD-induced coma arising from anaesthesia or acute
    overdose.  However, the use of flumazenil has not been shown to reduce
    mortality or sequelae in such cases.  As the mortality in pure BZD
    poisoning is extremely low, studies with mortality as end-point are
    impractical since a reasonable level of statistical significance could
    probably never be obtained.  However, in cases of mixed intoxication,
    especially with ethanol and triazolam/flunitrazepam, the use of
    flumazenil may be life-saving due to the poten-tiation of BZD toxicity
    by ethanol.  Given this situation, it is obvious that the routine use
    of flumazenil in BZD poisoning is not indicated and that
    recommendations for its use in clinical toxicology must be based on
    pragmatic considerations made by clinicians experienced in treating

    these patients.  Flumazenil is a relatively expensive drug and this
    may also influence its use, especially in areas with limited

         The use of flumazenil in BZD poisoning should, therefore, only be
    advocated in situations with complications, which are rarely seen
    except in cases of mixed ingestion.  Although not of life-saving
    significance, it also seems reasonable to advocate the use of
    flumazenil if intubations (before gastric lavage) and mechanical
    ventilation can thereby be avoided (see section 3.13.1).  The proposed
    uses of flumazenil within acute medicine and anaesthesia are listed in
    section 3.13.1.  Acute poisoning is always an important differential
    diagnosis in cases of coma in children and young adults.  The
    diagnostic use of flumazenil in such cases can be justified by its
    high therapeutic index and the fact that this may limit the use of
    other diagnostic procedures such as cerebral CT scan, clinical
    chemistry analyses and even lumbar puncture.

    3.12.2  Dosage and route

         Flumazenil is available for intravenous and oral administration. 
    The need for the latter formulation may be questioned in view of the
    fact that drugs should generally be given intravenously in the
    emergency situation and the bioavailability is low and variable.  Thus
    the intravenous route is preferable.  Doses need to be adjusted
    according to individual clinical response, bearing in mind the very
    high therapeutic index of flumazenil.

    a)   In anaesthetics and in intensive care, doses of 0.2-0.5 mg should
         be used to reduce sedation and doses of 0.5-1 mg to abolish other
         BZD effects (Amrein, 1987).

    b)   In cases of BZD overdosage, single doses of 0.3-1 mg can be given
         and repeated as necessary.  If there is no clinical response to
         2 mg flumazenil given over a period of 5-10 minutes, diagnoses
         other than BZD poisoning are likely.  It is also possible to
         administer a continuous infusion (0.3-1 mg/h) of flumazenil
         (diluted in 0.9% sodium chloride solution or 5% glucose solution)
         in patients relapsing into a coma and/or respiratory depression
         following an initial effect of flumazenil injection.

    c)   In children, experience is limited and dosage regimens less well
         documented (Lheureux & Askenasi, 1988; Wood  et al., 1987).  It
         is suggested that intravenous doses of 0.1 mg should be given
         once per minute until the child is awake.  It may be necessary to
         give a subsequent continuous intravenous infusion at a rate of
         0.1 to 0.2 mg/h.

    3.12.3  Other consequential or supportive therapy

         Treatment with flumazenil requires continuous intensive
    observation. After the administration of a single dose of flumazenil,
    the patient must be observed for at least 2 h to be certain that BZD-
    induced complications will not recur.  The termination of continuous
    infusion requires intensive care monitoring.

    3.12.4  Areas where there is insufficient information to make

         There is insufficient information to make recommendations in the
    case of hepatic encephalopathy (indication is based on the hypothesis
    that hepatic encephalopathy is associated with increased GABA-mediated
    inhibitory neurotransmission).

    3.12.5  Proposals for further study

         The use and dosages of flumazenil in children require further
    study.  Indications for utilization of oral preparations need to be
    clarified.  The use in coma of unknown origin merits further studies.

    3.12.6  Adverse effects

         The most frequent adverse effects have been reviewed by Amrein
    (1987).  When flumazenil is used in anaesthesia, the main adverse
    effects that have been reported are nausea and vomiting (placebo:
    7.5%; < 1 mg flumazenil: 12.1%; 1-10 mg flumazenil: 24.5%).  Other
    adverse effects, which have been reported in less than 5% of cases,
    are tremor, involuntary movements, dizziness, agitation, discomfort,
    tears, anxiety, and a sensation of cold.

         Minor effects occur when flumazenil is used in intensive care,
    where agitation is the commonest adverse effect (10%).  When it is
    administered to patients showing BZD habituation, the following
    features occur: anxiety, tenseness, fear, agitation, confusion,
    convulsions (Marchant & Wray, 1989) and myoclonic seizures.  Their
    frequency and intensity depend on the degree of dependency and they
    are believed to be related to some sort of BZD abstinence syndrome.

         When administered rapidly, flumazenil can cause hypertension,
    tachycardia and acute anxiety.  This equivalent of an "exercise test"
    was observed with the 1 mg/ml solution, which is no longer used.

    3.12.7  Restrictions of use

         In certain circumstances, BZD antagonism by flumazenil may be

    a)   An acute withdrawal syndrome can occur in patients showing BZD
         habituation following therapy or abuse.

    b)   Convulsions can occur in cases of mixed drug overdosage where BZD
         has been taken with a drug liable to cause convulsions (such as
         a tricyclic antidepressive agent).

    c)   Convulsions can be induced in patients treated with BZD for
         seizure disorders or in patients who for years have been using
         BZD for sleep disturbances.

         There are other limitations to the use of flumazenil.

    a)   It has a short-lived effect and repeated injection or continuous
         infusion is often necessary unless a short-acting BZD (e.g.,
         triazolam) has been ingested.

    b)   In cases of mixed drug overdosage, the patient may remain
         unresponsive when other drugs are contributing to the coma.

    c)   The treatment costs are high and supportive treatment may be

    3.13  Model Information Sheet

    3.13.1 Uses

         Flumazenil is a specific antagonist of the effects of BZD at
    central GABA-ergic receptors.

         Within the domains of intensive care and anaesthesia, flumazenil
    may be valuable in the following circumstances:

    a)   to diagnose BZD-induced unconsciousness in patients presenting
         coma of unknown origin;

    b)   to terminate long-term BZD-induced sedation in the intensive care
         unit (e.g., weaning from ventilatory support);

    c)   to reduce BZD-induced sedation or to counteract paradoxical
         anxiety reactions to BZD in anaesthesia;

    d)   to antagonise BZD-induced sedation after short diagnostic
         procedures where a long-acting BZD has been used.

         Flumazenil may be justified in the following situations in cases
    of BZD poisoning:

    a)   to facilitate gastric lavage and avoid intubation in comatose

    b)   to treat complications in severe cases of mixed poisoning where
         BZD is thought to be one of the major toxic agents;

    c)   to avoid the need for mechanical ventilation in cases where there
         is respiratory depression.

         The routine use of flumazenil for the treatment of BZD overdosage
    is not recommended.

    3.13.2  Dosage and route

         The intravenous route of administration is recommended when
    flumazenil is given as a BZD antagonist.  Doses need to be adjusted
    according to individual clinical response and the following are

    a)   In anaesthetics and in intensive care (adults), doses of 0.2-0.5
         mg should be used to reduce sedation and doses of 0.5-1 mg to
         abolish BZD effects.

    b)   In cases of BZD overdosage (adults), single doses of 0.3-1 mg can
         be given and repeated as necessary.  The absence of clinical
         response to 2 mg flumazenil within 5-10 min indicates that BZD
         poisoning is not the major cause of coma and other complications. 
         It is also possible to administer a continuous infusion (0.3 to
         1 mg/h) of flumazenil (diluted in 0.9% sodium chloride solution
         or 5% glucose solution) following an initial response to

    c)   In children, it is suggested that intravenous doses of 0.1 mg
         should be given once per minute until the child is awake.  It may
         be necessary to give a subsequent continuous intravenous infusion
         at a rate of 0.1 to 0.2 mg/h.

    3.13.3  Precautions/contraindications  Pharmaceutical precautions

         Solutions of flumazenil should be stored at +4 °C.  No other drug
    should be injected or infused with the flumazenil, which should be
    made up in 0.9% sodium chloride or 5% glucose (dextrose) solution.  Other precautions

         Treatment with flumazenil requires continuous intensive
    observation. After the administration of a single dose of flumazenil,
    the patient must be observed for at least 2 h to be certain that
    BZD-induced complications will not recur.  The termination of
    continuous infusion requires intensive care monitoring.

         Note that in cases of mixed drug overdosage, the patient may
    remain unresponsive where other drugs are contributing to the coma.

         BZD antagonism by flumazenil may in certain circumstances be

    a)   An acute withdrawal syndrome can occur in patients showing BZD
         habituation following therapy or abuse.

    b)   Convulsions can occur in cases of mixed drug overdosage where BZD
         has been taken with a drug liable to cause convulsions (such as
         a tricyclic antidepressive agent).

    c)   Convulsions can be induced in patients treated with BZD for
         seizure disorders.

         The three above-mentioned situations may be considered relative
    contraindications to its use; flumazenil should only be used when it
    is strongly indicated.  In these situations, it should be given more
    slowly than usual (e.g., 0.3 mg intravenously over 3 min, a 3-min
    pause, then a further 0.3 mg at the same rate, and so on).

    3.13.4  Adverse effects

         Various effects have been reported when flumazenil is used in
    anaesthesia.  These include (in order of decreasing frequency):
    nausea, vomiting, tremor, involuntary movements, dizziness, agitation,
    discomfort, tears, anxiety, and sensation of cold.

         Similar effects occur when flumazenil is used in intensive care,
    agitation being the commonest adverse effect.  When flumazenil is
    administered to patients showing BZD habituation, the following can
    occur: anxiety, tenseness, fear, agitation, confusion, convulsions and
    myoclonic seizures.

         When administered rapidly, flumazenil can cause hypertension,
    tachycardia and acute anxiety.

    3.13.5  Use in pregnancy and lactation

         Even though animal studies showed no embryotoxicity or
    teratogenicity at high doses, flumazenil, like any new drug, should be
    avoided at the beginning of pregnancy.  However, in life-threatening
    situations its possible risk to the fetus is probably far outweighed
    by its beneficial effects.  Isolated administration of flumazenil
    during lactation is not contraindicated.

    3.13.6  Storage

         No special storage conditions are required.

    3.13.7 Special risk groups

         Acute withdrawal syndrome can occur in patients showing BZD
    habituation following therapy or abuse (see section 3.13.3).

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    effects of the benzodiazepine antagonist Ro 15-1788 following mixed
    anaesthesia in association with flunitrazepam, compared with a
    placebo: a double-blind study.] Beitr Anaesthesiol Intensivmed, 35:
    121 (in German).

    Wood C, Bismuth C, Oriot D, Devictor D, & Juault G (1987) 
    Réversibilité d'un coma par benzodiazépine par perfusion de flumazenil
    chez un enfant. Presse Méd, 16: 1483.

    Ziegler WH & Schalch E (1983)   Antagonism of benzodiazepine-induced
    sedation in man.  In: In sleep. Proceedings of the 6th European
    Congress of Sleep Research, Zurich, 1982. Basel, Karger, pp 427-429.


    4.1  Introduction

         Dantrolene sodium, a hydantoin-furan derivative, causes skeletal
    muscle relaxation by preventing calcium flux across the sarcoplasmic
    reticulum.  It was first synthesized in 1967 and the initial use was
    to treat muscle spasm (Dykes, 1975).  More recently dantrolene has
    been used successfully in the treatment of malignant
    hyperpyrexia/hyperthermia and neuroleptic malignant syndrome,
    hypercatabolic syndromes that have previously been associated with
    high mortality rates.

         Malignant hyperthermia results from a genetic susceptibility to
    certain anaesthetic agents (autosomal dominant myopathy), and is
    usually fatal unless appropriate treatment is given.  However,
    provided the diagnosis is made early and treatment with dantrolene and
    necessary supportive measures is given at once, there is rapid
    resolution of the hyperthermia.  Signs of malignant hyperthermia may
    occur from minutes to 1-2 h after the induction of anaesthesia and are
    thought to result from an acute influx of calcium into the muscle
    cytoplasm from the sarcoplasmic reticulum, which results in abnormal
    muscle contraction, hypermetabolism, hyperthermia and muscle damage.

         In patients with a family history or previous episodes of
    malignant hyperthermia, prophylactic treatment with dantrolene prior
    to anaesthesia has been advocated (Shime et al., 1988).  The
    prophylactic use of dantrolene with susceptible patients is, however,
    controversial.  Those opposing this approach advocate the agreed
    safety precautions and the availability of dantrolene in order to
    intervene promptly if any crisis occurs (Harrison, 1988; Hackl et al.,
    1990). At present, most anaesthesiologists do not use dantrolene
    prophylactically in these patients.

         The predisposition for malignant hyperthermia is probably
    heterogenous and not only linked to the CRC (calcium release channel)
    gene on chromosome 19 (Fagerlund et al., 1992).  It is therefore
    premature to use DNA markers flanking this gene as the major test to
    diagnose susceptibility to the malignant hyperthermia syndrome,
    although this has been suggested (Healy et al., 1991).  Predisposition
    to the disease is still best determined through a halothane- and
    caffeine-induced contracture test on a skeletal muscle biopsy
    (MacLennan et al., 1990).

         Neuroleptic malignant syndrome occurs in 0.2-1% of patients
    taking neuroleptics, especially when haloperidol and the depot
    fluphenazines are used (Pope et al., 1986).  One component of the
    syndrome appears to be sustained extrapyramidal rigidity causing
    hyperthermia and muscle necrosis (rhabdomyolysis).  The syndrome may
    last for 10-14 days or 4 weeks after cessation of oral or depot
    neuroleptics, respectively.

         Dantrolene has also been used successfully in the treatment of a
    few cases of heat-stroke (Lydiatt & Hill, 1981), which has many
    similarities to malignant hyperthermia.

         This monograph will restrict itself to the use of dantrolene in
    the treatment of drug-induced hypercatabolic syndromes.

    4.2  Name and Chemical Formula of Antidote

    Dantrolene sodium
    IUPAC name:                   1-[[5-( p-nitrophenyl)
                                  furfurylidene]amino]hydantoin sodium

    Empirical formula:            C14H9N4NaO5 (anhydrous salt)

    Relative molecular mass:      336 (anhydrous salt)

         The hydrated salt contains approximately 15% water (3´ moles) and
    has a molecular weight of 399.

    CAS numbers:                  7261-97-4      Dantrolene

                                  14663-23-1     Dantrolene sodium,

                                  24868-20-0     Dantrolene sodium salt,
                                                 (Martindale, 1989)

    Molecular structure:


    Proprietary names:            DantriumR (Norwich Eaton UK,
                                  Australia, Belgium, Canada, France,
                                  Netherlands, New Zealand, South Africa,
                                  USA) (Martindale, 1989).
                                  DanleneR (SIT, Italy)
                                  DantamacrinR (Röhm Pharma, D-6108
                                  Boehringer Mannheim, Switzerland)
                                  DantralenR (Lafarquim, Spain)
                                  DantriumR (Norwich Eaton, Norwich NY
                                  13185, USA;
                                  Formenti, I-20149 Milan, Italy; Smith
                                  Kline & French, USA; Yamanouchi, Japan)
                                  DantrixR (SIT, I-27035 Mede, Italy)
                                  (Martindale, 1989;
                                  Index Nominum, 1990)

    4.3  Physico-chemical Properties

         Dantrolene sodium is an orange, odorless powder with a melting
    point of 279-280 °C.  It is slightly soluble in water, but it
    hydrolyses and precipitates the extremely insoluble (< 1 mg/l) free
    acid, dantrolene.  This hydrolysis may be prevented to some extent by
    the addition of small amounts of sodium hydroxide, but this procedure
    is complicated by the precipitation of dantrolene sodium by the common
    ion effect.  The amount remaining in solution is a function of the
    total ionic strength.

         The approximate solubility data given in Table 1 were obtained at
    room temperature.

    Table 1.  Solubility of Dantrolene sodium in various solvents


    Solvent                          Solubility (g/l)

    Propylene glycol                 40
    Glycerine                        25
    Polyethylene glycol 400          80
    Dimethylformamide                15a
    Dimethylacetamide                15a
    0.2% Morpholine in water         0.2
    1% Morpholine in water           0.5
    2% Morpholine in water           0.9
    Chloroform                       < 20 (70 g/l for dantrolene)
    Acetone                          20-25

    a  complex formed

         Dantrolene (the free acid of dantrolene sodium) is a weak acid
    with a pKa of about 7.5.  However, the extremely low solubility of the
    free acid prevents an accurate determination of its pKa (personal
    communication from A.W. Castellion, Norwich Easton, to the IPCS).

         Dantrolene sodium solutions should be protected from light. 
    Dantrolene sodium capsules and powder for injection should be kept at
    a temperature below 40 °C, preferably between 15 and 30 °C, and the
    capsules should be stored in well-closed containers.  Following
    reconstitution with 60 ml of sterile water for injection, dantrolene
    sodium injection solution is stable for 6 h when stored at 15-30 °C
    and protected from light.

         The excipients used with dantrolene are mannitol and sodium

    4.4  Pharmaceutical Formulation and Synthesis

         Dantrolene sodium is available as capsules of 25 mg, 50 mg and
    100 mg.

         It is also available as an orange powder for preparing injections
    in vials of 20 mg, with 3 g mannitol and sodium hydroxide.  The powder
    is dissolved by the addition of 60 ml of water, producing a highly
    irritant solution with a pH of about 9.5.

         Snyder et al. (1967) described the synthesis of a series of 1-
    [(5-arylfurfurylidene)amino]hydantoins from the appropriate
    aryldiazonium chlorides and 2-furaldehyde, coupled in aqueous acetone
    with cupric chloride as the catalyst.  The intermediate aldehydes were
    condensed directly with 1-aminohydantoin hydrochloride to give the
    aminohydantoin derivatives.

    4.5  Analytical Methods

    4.5.1  Identification and quantification of dantrolene sodium and its

         The thin-layer chromatography details are as follows:

    *    layer:           silica gel G, 250 µm thick

    *    mobile phase:    chloroform:acetone (4:1), retention factor: 19;

                          ethyl acetate:methanol:strong ammonia solution
                          (85:10:5), retention factor: 0.9;

                          ethyl acetate, retention factor: 36 (Moffat,

         An alkaline solution of dantrolene sodium gives a peak in the
    ultraviolet spectrum at 314 nm (Moffat, 1986).  In the infrared
    spectrum, principal peaks occur at the following wavenumbers: 1600,
    1225, 1510, 850, 1713, 1108 (dantrolene sodium, KBR disc) (Moffat,

         Saxena et al. (1977) reported a method for the determination of
    dantrolene sodium in a dosage form by converting the drug to its free
    acid in acidic media (pH 2.5-4.0) using 2N HCl.  This is followed by
    extraction into a 1-butanol-chloroform mixture and quantification by
    high-performance liquid chromatography (HPLC) using carbon
    tetrachloride:dimethylformamide (90:10) as mobile phase.  The peaks
    are detected at 375 nm.

    4.5.2  Quantification of dantrolene in body fluids  Spectrofluorimetry

         This is a rapid and sensitive method for the quantitative
    determination of dantrolene in plasma, blood and urine, and consists
    of a direct extraction of dantrolene into a nitropropane-heptane (1:1)
    solvent mixture.  The excitation peak is at 395 nm and the
    fluorescence peak at 530 nm (Hollifield & Conklin, 1968).  The
    sensitivity is 100 ng/ml in plasma, blood and urine, and 400 ng/ml in
    bile and tissue (Moffat, 1986)  High-performance liquid chromatography

         Dantrolene and its metabolites 5-hydroxydantrolene and
    nitroreduced acetylated dantrolene (F490) are detected by a reversed-
    phase HPLC method after a preliminary extraction step into a
    chloroform-butanol mixture for plasma samples.  The detection limit is
    20 ng/l (Wuis et al., 1983).

         Lalande et al. (1988) have reported an alternative method for the
    determination of dantrolene and its reduced and oxidized metabolites
    in plasma.

    4.6  Shelf Life

         The following instructions for storage conditions are recommended
    by the manufacturer:

        Dosage form        Storage requirements     Shelf-life


    As supplied        below 30 °C              3 years

    Reconstituted      15-30 °C                 6 h when protected from
    4.7  General Properties

         Dantrolene is a peripheral striated muscle relaxant agent which
    most probably acts by preventing calcium flux across the sarcoplasmic
    reticulum, thereby reducing the intracellular free calcium
    concentration (Lopez et al., 1987).  Its site of action is in the
    muscle itself, beyond the motor end-plate.  Although this mechanism of
    action seems logical, other authors stress that we are still a long
    way from understanding the finer details of its mode of action and,
    correspondingly, those of the pathogenesis of malignant hyperthermia
    (Harrison, 1988).  The genetic defect in susceptible individuals is
    considered to reside in the calcium release channel (CRC) of the
    sarcoplasmic reticulum of skeletal muscle (MacLennan et al., 1990).

         The effects of dantrolene on other calcium-dependant systems seem
    negligible at doses in current use (Hall et al., 1982).

    4.8  Animal Studies

    4.8.1  Pharmacodynamics  Effect on skeletal muscle

         Dantrolene inhibits the development of tension in animal muscle
    preparations  in vitro caused by caffeine or by depolarization.  The
    effect of dantrolene can be antagonized by raising the extracellular
    calcium concentration (Ellis & Wessells, 1977; Yamamoto et al., 1977;
    Anderson et al., 1978; Nelson, 1983).

         Dantrolene also inhibits the contractile response to ryanodine,
    which is known to cause release of calcium from skeletal muscle
    sarcoplasmic reticulum  (Fairhust et al., 1980).

         Dantrolene, therefore, probably inhibits skeletal muscle
    contraction by preventing release of Ca2+ from sarcoplasmic
    reticulum.  The results obtained by Ohta et al. (1990), using skinned
    skeletal muscle from guinea-pigs, suggested that dantrolene acts as a
    selective inhibitor of the calcium-induced Ca2+ release mechanism
    without having an effect on the Ca2+ pump of the sarcoplasmic
    reticulum or on the contractile machinery of skeletal muscle.

         Dantrolene also diminishes exercise-induced muscle damage in the
    rat, as judged from creatine kinase isoenzyme patterns in plasma
    before and after a 2-h run on a treadmill (Amelink et al., 1990).  Effects on other tissues

         The effects of dantrolene on cardiac muscle, smooth muscle, the
    nervous system and endocrine glands have been studied in animal
    experiments, and the data have been reviewed by Ward et al. (1986). 
    These data are not of clinical importance.  Studies in malignant hyperthermia-susceptible pigs

         Certain breeds of pig exhibit a stress-related syndrome very
    similar to that of anaesthetic-induced malignant hyperthermia in
    humans, and they are a useful investigational model for malignant

         Dantrolene inhibits contractures of skeletal muscle preparations
    induced by halothane, caffeine, suxamethonium, and potassium chloride
    and thymol (Okumura et al., 1980; Sullivan & Denborough, 1981). It
    also prevents the accumulation of myocytoplasmic calcium in the
    mitochondria of pigs susceptible to malignant hyperthermia
    (Stadhouders et al., 1984) and decreases the release of calcium from
    the sarcoplasmic reticulum of muscle from susceptible pigs (Ohnishi et
    al., 1983).  The reduction of the free intracellular calcium
    concentration is probably the mechanism of action of dantrolene in
    these animals (Lopez et al., 1987).  It has been suggested that
    dantrolene may act at the initial stage of excitation (Miyamoto &
    Racker, 1982).

         Dantrolene has been demonstrated to be effective in treating
    malignant hyperthermia induced by halothane or suxamethonium
    anaesthesia in susceptible pigs (Gronert et al., 1976; Harrison, 1977;
    Kerr et al., 1978; Hall et al., 1982).  It is also effective when
    given prophylactically before the induction of anaesthesia (Harrison,
    1977; Kerr et al., 1978).

    4.8.2  Pharmacokinetics

         The pharmacokinetics of dantrolene have been studied in human
    volunteers and this limits the need for animal data in this area.

         Following a single oral dose of 5 mg/kg in dogs and 1 mg/kg in
    rats, 20% and 29%, respectively, is absorbed (Fournier, 1982).

    4.8.3  Toxicology  Acute toxicity

         The oral LD50 has been estimated to be 29 g/kg in newborn rats. 
    No deaths  occurred after the oral administration of 8 g/kg to young
    adult rats, mice, hamsters and rabbits (Fournier, 1982).

         The LD50 after the intraperitoneal injection of dantrolene was
    780 mg/kg in rats (Fournier, 1982) and 1400 mg/kg in mice (Ellis &
    Carpenter, 1974).  The intravenous LD50 was > 40 mg/kg in rats and
    > 80 mg/kg in mice (Fournier, 1982).  Subacute toxicity

         Four out of 20 mice given dantrolene (84 mg/kg per day) by mouth
    for one month developed hepatic steatosis.  Renal tubular damage,
    crystal deposition in the renal tract, and hepatocellular necrosis
    were seen in rats after they had received oral doses of 60 to 500
    mg/kg per day for one month (Fournier, 1982).  Intraperitoneal doses
    of 50 mg/kg per day lowered the level of serum glucocorticoids over 5
    days (Francis & Hamrick, 1980).  No anatomical or histological changes
    were seen after one month with oral doses of up to 500 mg/kg per day
    in dogs or 90 mg/kg per day in monkeys, although animals given high
    doses developed anorexia, hypotonia and weight loss (Fournier, 1982).  Chronic toxicity

         Rats receiving oral dantrolene doses of 15 mg/kg per day or more
    showed a reduction in weight gain, hepatocellular degeneration,
    crystalluria and keratitis with corneal opacities.  Females developed
    mammary tumours, with a statistically significant increase in the
    incidence of breast adenocarcinoma in those receiving 60 mg/kg per day
    (Fournier, 1982).

         Dogs showed no effects when treated with dantrolene (15 mg/kg per
    day) for 12 months.  However, higher doses caused a reduction in
    weight gain, and at 60 mg/kg per day impaired hepatocellular function,
    anaemia and crystalluria were apparent.  One case of intrahepatic
    cholestasis occurred (Fournier, 1982).  Teratogenicity

         There was no evidence of teratogenic effects from dantrolene when
    doses of up to 45 mg/kg per day were given to rats, rabbits or monkeys
    (Pinder et al., 1977).

         Using the maternal-fetal sheep model in nine pregnant ewes, Craft
    et al. (1988) found an equilibrium between maternal and fetal plasma
    dantrolene concentrations 5 min after dosing.  The fetal level of
    dantrolene was about 10% of that of the mother.  It was concluded that
    the administration of intravenous dantrolene (1.2 or 2.4 mg/kg) had no
    clinically significant adverse effect on mother or fetus in the sheep

    4.9  Volunteer Studies

         Included in this section are studies involving healthy volunteers
    and patients undergoing surgery from whom informed consent was

    4.9.1  Administration and plasma concentrations

         Peak plasma dantrolene concentrations of 0.5 to 0.95 mg/l
    occurred 4 to 8 h after 50 mg dantrolene was administered orally to
    six healthy volunteers.  The corresponding peak 5-hydroxydantrolene
    concentration was 0.11 to 0.3 mg/l after 6 to 8 h (Katogi et al.,
    1982).  In the study of Allen et al. (1988), a total oral dose of 5 mg
    dantrolene/kg was given to ten malignant hyperthermia-susceptible
    patients prior to anaesthesia.  All subjects had plasma dantrolene
    levels above 2.8 mg/l, indicating a high bioavailability of

         In six patients, who had previously suffered from suspected or
    proven malignant hyperthermia and who received prophylactic
    intravenous dantrolene (2.5 mg/kg) before anaesthesia, peak blood
    concentrations of 4.3 to 6.5 mg/l were found (Flewellen & Nelson
    1985).  Lerman et al. (1989) infused dantrolene (2.4 mg/kg) over 10
    min in 10 children susceptible to malignant hyperthermia.  Mean
    dantrolene blood concentrations 1 min and 1 h after infusion were 6.03
    mg/l (SD ± 0.93) and 3.56 (SD ± 0.49) mg/l, respectively.  The blood
    concentrations of the metabolite 5-hydroxydantrolene rose to a maximum
    of 0.6 mg/l at 8 h and then fell with an apparent half-life of 9 h.

         Plasma dantrolene concentrations during prolonged treatment are
    similar to those found after single oral dosing (Vallner et al., 1979;
    Meyler et al. 1981). Metabolite concentrations may be relatively
    elevated after prolonged (> 2 months) administration (Vallner et al.

    4.9.2  Distribution

         In the 10 children studied by Lerman et al. (1989), the apparent
    volume of distribution for dantrolene was 0.54 l/kg (SD ± 0.08).   In
     vitro studies show that dantrolene interacts with human serum
    albumin at a minimum of two sites on the protein (Vallner et al.,
    1976), but exact figures for the degree of protein binding have not
    been reported.  Distribution to the fetus and newborn baby

         The oral administration of dantrolene (total doses of 250 and 600
    mg) to two pregnant patients thought to be susceptible to malignant
    hyperthermia resulted in a fetal/maternal serum concentration ratio of
    approximately 0.4, thus indicating that this agent reaches the
    placenta in appreciable concentrations (Morison 1983).  In a study of
    20 pregnant women susceptible to malignant hyperthermia, the mean
    maternal predelivery dantrolene level was 0.99 ± 0.5 mg/l and the mean
    neonatal cord blood dantrolene level 0.68 ± 0.3 mg/l (Shime et al.,

    4.9.3  Elimination

         The major metabolite of dantrolene in humans is
    5-hydroxydantrolene, produced by hepatic microsomal oxidation,
    although minor metabolites also exist (Lietman et al., 1974; Ellis &
    Wessels, 1978).  According to  in vitro data, this major metabolite
    is half as potent as the parent drug, whereas the other metabolites
    appear to be inactive (Ellis & Wessels, 1978).  When dantrolene is
    administered orally, 15-25% of the dose is excreted renally,
    predominantly as 5-hydroxydantrolene but with small amounts of reduced
    acetylated dantrolene and unchanged drug (Lietman et al., 1974).

         The elimination half-life of orally administered dantrolene in
    humans is probably between 6 and 9 h, although values of 3 to 22 h
    have been observed (Lietman et al., 1974; Dykes 1975; Meyler et al.,
    1979, 1981; Wuis et al., 1983; Allen et al., 1988).  The elimination
    half-life after intravenous dosing was reported to be 12 h in both
    healthy volunteers (Flewellen et al., 1983) and patients known to
    suffer from malignant hyperthermia (Flewellen & Nelson, 1985).  This
    is in accordance with the value of 10 h (SD ± 2.6) reported in
    children (Lerman et al., 1989).  In the study by Shime et al. (1988)
    in neonatals, the dantrolene half-life was 20 h.

         The median elimination half-life for 5-hydroxydantrolene, the 
    major metabolite of dantrolene, was found to be 15.5 h (range, 8.1 to
    29.4 h) in healthy volunteers (Meyler et al., 1979), whereas it was 9
    h (SD ± 2.5) in the 10 children studied by Lerman et al. (1989).

    4.9.4  Human in vitro pharmacodynamics

         Dantrolene inhibits the contraction of isolated human skeletal
    muscle induced by halothane or suxamethonium (succinylcholine) (Nelson
    & Denborough 1977; Hallsall & Ellis 1979; Fletcher & Rosenberg 1985).

    4.10  Clinical Studies - Clinical Trials

         The rarity of malignant hyperthermia, the variability of its
    clinical manifestations and the range of adjunctive therapy have

    precluded controlled trials or comparative studies of dantrolene in
    its treatment.

    4.11  Clinical Studies - Case Reports

         This section presents several case reports where the use of
    dantrolene is associated with a favourable outcome.  Even if some of
    the case reports (or series of such reports) may seem convincing,
    regarding the efficacy of dantrolene, one should still bear in mind
    the lack of controlled studies.

    4.11.1  Use in malignant hyperthermia

         Ward et al. (1986) and Harrison (1988) have reviewed the
    published case reports.  In children, an initial intravenous dose of
    1 mg/kg has usually been effective if given within 2 h of the onset of
    signs and symptoms, although a boy of 11 years died in spite of
    receiving dantrolene (1 mg/kg) about 2 h after the onset of malignant
    hyperthermia (Desparmet et al., 1983).  Doses of up to 3.6 mg/kg have
    been given to patients who subsequently recovered (Maruta et al.,
    1980). Experienced clinicians prefer a more aggressive dosing of 1
    mg/kg per min up to a total of 10 mg/kg or even more (personal
    communications by B.A. Britt and T. Fagerlund to the IPCS, 1992).  The
    time factor is critical, since dantrolene is often ineffective if
    treatment is delayed for 2 h after the onset of signs in children
    (personal communication by B.A. Britt to the IPCS, 1992).

         In adults, dantrolene appears uniformly effective if given within
    6 h of the precipitating anaesthetic agent, but death may supervene if
    treatment is delayed beyond this (Kolb et al., 1982; personal
    communication by B.A. Britt to the IPCS, 1992).  Death occurred in one
    case despite a massive initial intravenous dose (Mathieu et al., 1979)
    and in two others despite prolonged oral and intravenous therapy over
    10 to 21 days (Kolb et al., 1982).  Presumably irreversible changes
    took place before treatment was started.  In the study by Kolb et al.
    (1982), intravenous dantrolene (a total dose of 1-7 mg/kg) lead to the
    successful treatment of three patients with probable and eight
    patients with unequivocal malignant hyperthermia.  Prophylaxis of malignant hyperthermia

         Where a family history of malignant hyperthermia has been
    particularly strong or where a patient has had previous confirmed or
    suspected episodes of anaesthetic-induced malignant hyperthermia, the
    prophylactic administration of dantrolene has been discussed, along
    with the avoidance of "trigger" agents (Ward et al., 1986).  An oral
    dosage of 4 to 8 mg/kg per day, given in three or four divided doses
    for 1 or 2 days with the last dose being administered 3 to 4 h prior
    to anaesthesia, has been recommended (Ward et al., 1986). 
    Alternatively, a single intravenous dose of 2.5 mg/kg has been
    proposed, to be given just prior to surgery (Flewellen et al., 1983).

         Most of the patients treated in this manner have undergone
    uneventful surgery although in three cases postoperative tachycardia,
    increased blood pressure, and respiratory and metabolic acidosis
    occurred without hyperthermia or muscle rigidity.  These patients were
    all successfully treated with either further intravenous dantrolene
    (Fitzgibbons, 1981; Ruhland & Hinkle, 1984) or by correcting the
    metabolic acidosis (de Pinna, 1978).

         There is, however, no consensus on this prophylactic use of
    dantrolene (Harrison, 1988) although most experienced clinicians are
    now in favour of using no prophylactic treatment (personal
    communication by B.A Britt and T. Fagerlund to the IPCS, 1992). 
    Recently, a series of 30 general anaesthesias in 24 patients
    susceptible to malignant hyperthermia was reported.  In all patients,
    malignant hyperthermia susceptibility was confirmed by  in vitro
    testing of skeletal muscles obtained from a biopsy of the quadriceps
    femoris muscle, and four patients had experienced previous episodes of
    malignant hyperthermia during anaesthesia.  No clinical or biochemical
    features of malignant hyperthermia were observed (Hackl et al., 1990). 
    These authors concluded that safe anaesthesia for these patients could
    easily be provided simply by avoiding trigger agents and carefully
    preparing the monitoring equipment and anaesthesia machine. 
    Dantrolene should be reserved for the treatment of malignant
    hyperthermia.  Prophylaxis of malignant hyperthermia during pregnancy

         In a prospective study of 32 pregnant women known to be
    susceptible to malignant hyperthermia, 17 received oral dantrolene
    sodium beginning 5 days prior to planned delivery, while the other 15
    did not receive prophylactic dantrolene.  Malignant hyperthermia
    developed immediately postpartum in one mother and her baby who had
    not received prophylactic dantrolene, but both mother and baby
    responded rapidly to intravenous dantrolene.  None of the other
    pregnancies was complicated and all fetal examinations and neonatal
    neurological assessments were normal (Ward et al., 1986).

         In a series of 20 malignant hyperthermia-susceptible pregnant
    patients, dantrolene was given orally for 5 days before and 3 days
    after delivery (in three cases, delivery was by Caesarean section)
    (Shime et al., 1988).  No signs of malignant hyperthermia or adverse
    effects of dantrolene were seen in this non-controlled study.

         There have been several other case reports of successful use of
    prophylactic intravenous dantrolene in pregnant women who were
    susceptible to this condition and  who underwent anaesthesia during
    birth (Cupryn et al., 1984; Glassenberg & Cohen, 1984) and of the
    reversal of established malignant hyperthermia with intravenous
    dantrolene in both mothers and their neonates (Sewall et al., 1980;
    Lips et al., 1982).  Weingarten et al. (1987) reported a case of

    postpartum uterine atony in a patient who received dantrolene during
    a Caesarian section.

         Although there are several non-controlled  reports of the
    successful use of dantrolene prior to planned delivery, there is no
    established consensus on this use.

    4.11.2  Use in neuroleptic malignant syndrome

         In the neuroleptic malignant syndrome, thermogenesis is
    ultimately due to tonic contraction of skeletal muscles.  Thus, the
    use of dantrolene may be helpful by relaxing skeletal muscle.

         Since the initial observations (Bismuth et al., 1982; Boles et
    al., 1982), there have been many case reports of the use of dantrolene
    in the neuroleptic malignant syndrome (Ward et al., 1986; Harrison
    1988) with no consensus concerning dosage.  Single intravenous bolus
    doses (less than 3 to 10 mg/kg) and repeated oral doses (25 to 600
    mg/day)  have been used, often in combination with other drugs and
    supportive treatment.  Dantrolene apparently reduces the pyrexia,
    usually within 12 h of intravenous therapy and over a somewhat longer
    period with oral dantrolene therapy.  Most patients also improve
    clinically, although this occurs at a later stage.  In some cases
    withdrawal of oral dantrolene therapy has been associated with a
    deterioration of the patient's condition and an increase in body

    4.11.3  Use in other drug-induced hyperthermia

         Hyperthermia due to or associated with increased muscular
    rigidity can occur in poisoning with strychnine (Gordon & Richards,
    1979), phencyclidine (Jan et al., 1978) or Cicuta species (water
    hemlock) (Starreveld & Hope, 1975).  In cases of poisoning with these
    agents, the direct action of dantrolene on muscle activity is likely
    to be of benefit in controlling the hyperpyrexia.  It would be logical
    to give intravenous dantrolene as in cases of malignant hyperthermia,
    provided it was combined with standard supportive measures such as
    external cooling.  There is, however, no experimental verification of
    this view, nor any report of a relevant clinical case.

         Amphetamines (Jordan & Hampson, 1960; Kendrick et al., 1977;
    Ginsberg et al., 1970), monoamine oxidase inhibitors (Mirchandani &
    Reich, 1985), lysergic acid diethylamide (Friedman & Hirsch, 1971;
    Mercieca & Brown, 1984), and cocaine (Roberts et al., 1984) all cause
    hyperthermia, which is due at least in part to motor overactivity with
    or without convulsions.  Where hyperthermia does not respond to
    sedation with a major tranquillizer, and where paralysis and
    artificial ventilation are inappropriate or ineffective, dantrolene
    should be of benefit, but documentation is still lacking.

         A case of overdosage with phenelzine, a monoamine oxidase
    inhibitor, was treated successfully with intravenous dantrolene after
    conventional therapy had failed (Kaplan et al. 1986), as was a case of
    carbon monoxide poisoning with hyperthermia and rigidity (Holter &
    Schellens, 1988).  In a fatal case of theophylline poisoning with
    rhabdomyolysis, dantrolene administration was claimed to be useful in
    controlling the hypermetabolic state (Parr & Willatts, 1991).

         Hyperthermia in poisoning with salicylates, dinitrophenol and the
    herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is due to uncoupling
    of oxidative phosphorylation.  Tricyclic antidepressives and other
    anticholinergic drugs reduce sweating and so impair heat loss. 
    Dantrolene would  not be expected to have a role in the treatment of
    hyperpyrexia induced by these mechanisms.

    4.12  Summary of Evaluation

    4.12.1  Indications  Treatment of malignant hyperthermia

         When combined with standard cooling and supportive therapy,
    dantrolene has proved effective in rapidly reversing clinical symptoms
    in anaesthetic-induced malignant hyperthermia, as judged from clinical
    case reports.  Failure of dantrolene to prevent the often fatal
    consequences of malignant hyperthermia is usually a consequence of
    late diagnosis and therapy.  Treatment of neuroleptic malignant syndrome

         Dantrolene may be helpful as an adjunct to supportive therapy in
    neuroleptic malignant syndrome induced by drugs such as dopamine
    antagonists, particularly the major tranquillizers.  There is no
    report of a controlled trial in this rare illness, and no study
    comparing dantrolene with bromocriptine, which has also been used in
    its management.  Treatment of hyperthermia induced by muscle rigidity in

         Though documentation is lacking, there are good theoretical
    grounds for using dantrolene to treat hyperthermia due to poisoning
    with strychnine, phencyclidine or Cicuta species (water hemlock).  It
    might also be useful in the management of hyperthermia in patients
    poisoned with amphetamines, cocaine, lysergic acid diethylamine (LSD)
    or monoamine oxidase inhibitors, where hyperthermia is associated with
    motor overactivity.

    4.12.2  Advised routes and doses  Treatment of severe drug-induced hyperthermia, including
              malignant hyperthermia

         Dantrolene (2.5 mg/kg) should be given intravenously as soon as
    possible.  A response to the treatment should be apparent within
    minutes; if not, up to 10 mg/kg may be given again every 15 min until
    there is an effect.  Subsequent to intravenous therapy, dantrolene (4
    mg/kg per day in divided doses for 48 h) can be given orally to
    prevent recurrence.  The patient should stay in the intensive care
    unit for at least 24 h after the hyperthermia reaction has subsided
    (personal communication by T. Fagerlund to the IPCS, 1992).  The
    proposed dosage regimen for dantrolene is not clearly defined (see
    section 4.12.4).

         In cases of neuroleptic malignant syndrome, the use of dantrolene
    and dopamine agonists (amantadine and bromocriptine) has been
    described (Boles et al., 1982; Goulon et al., 1983) and has produced
    promising results.  Prophylaxis of malignant hyperthermia prior to anaesthesia
              in susceptible patients

         Triggering anaesthetic agents have to be avoided in patients
    known to be susceptible to malignant hyperthermia.  Such agents are
    depolarizing muscle relaxants (succinylcholine), halogenated
    inhalational anaesthetics (e.g., halothane), haloperidol and
    promethazine.  Regional anaesthetic techniques should be preferred if

         Oral dantrolene (4-8 mg/kg per day) administered for 1-2 days
    prior to anaesthesia may prevent malignant hyperthermia in known
    susceptible individuals. Alternatively, intravenous dantrolene (2.5
    mg/kg) can be given just prior to anaesthesia (Flewellen et al.,
    1983).  Oral dantrolene given 5 days before and 3 days after delivery
    has been associated with favourable outcome in pregnant patients
    susceptible to malignant hyperthermia (Shime et al., 1988).  Such
    prophylaxis with dantrolene is controversial and not generally

    4.12.3  Other consequential or supportive therapy

         It is very important for the administration of dantrolene to be
    accompanied by the use of aggressive supportive therapy, including
    central cooling techniques, an inspired oxygen concentration enriched
    up to 100%, and correction of metabolic acidosis.  Serum potassium
    concentrations should be monitored closely.

         Further supportive therapy should be directed towards
    complications such as respiratory acidosis, cardiac arrhythmias, and
    instability of blood pressure.  Special attention must be given to the
    development of rhabdomyolysis leading to elevated serum muscle enzymes
    (creatine kinase, aspartate transaminase, aldolase).  If creatine
    kinase activities are above 10 000 U/l and/or meat-coloured urine is
    present, together with areas of swollen and tender skeletal muscles,
    the patient may develop acute renal failure as muscle debris is
    precipitated in the kidneys (myoglobinuria).  Associated electrolyte
    disturbances are hyperkalaemia, hypocalcaemia and hyperphosphataemia. 
    Acute renal failure of this nature has been reported to be prevented,
    even at creatine kinase activities above 70 000 U/l, when prompt
    forced alkaline diuresis treatment has been instituted in order to
    prevent debris deposition in the kidneys (personal communication by D.
    Jacobsen to the IPCS, 1992).  Urine output should exceed 2 ml/kg per
    h in these patients.

    4.12.4  Controversial issues and areas of insufficient information

         The prophylactic use of dantrolene prior to anaesthesia in
    susceptible patients should be considered controversial and an
    international consensus has yet to be established (Ward et al., 1986;
    Shime et al., 1988; Harrison, 1988; Hackl et al., 1990).  This use of
    dantrolene is not generally recommended (personal communications by T.
    Fagerlund and B.A. Britt to the IPCS, 1992).

         The dose regimen of dantrolene is not clearly defined.  The
    initial dose recommended in the USA is generally 1 mg/kg per min
    (personal communication by B.A. Britt to the IPCS, 1992), whereas the
    European recommendation is usually an initial dose of 2.5 mg/kg
    (personal communication by T. Fagerlund to the IPCS, 1992).  There is,
    however, a consensus on the maximum dose of 10 mg/kg per 15 min. 
    Furthermore, there is no clear overall maximum dose of dantrolene
    during the first hours of treatment.  This may be important, as
    malignant hyperthermia could be incorrectly diagnosed in places with
    limited laboratory facilities.  In such situations, one should not
    continue to give dantrolene in doses of 10 mg/kg per 15 min. 
    Therefore, if more than 20 mg/kg has been given during the first 30
    min without any effect, the diagnosis of malignant hyperthermia should
    certainly be questioned (personal communication by T. Fagerlund to the
    IPCS, 1992).  Another reason for lack of effect could be that
    dantrolene therapy has been initiated too late, since the time factor
    is critical.

         It is not clear whether doses higher than 10 mg/kg per day add
    any beneficial effects concerning the prognosis.  However, clinicians
    with experience in this field do recommend higher doses for critically
    ill patients who do not respond to the initial dose (personal
    communications by T. Fagerlund and B.A. Britt to the IPCS, 1992).

         The use of external cooling techniques with these patients has
    been generally recommended for years.  However, this treatment is now
    being questioned, since dantrolene treatment alone lowers temperatures
    to the normal range.  External cooling also prevents heat loss by
    inducing peripheral vasoconstriction and increases heat production by
    stimulating shivering and non-shivering thermogenesis (personal
    communication by B.A. Britt to the IPCS, 1992).

    4.12.5  Proposals for further studies

         The effect of dantrolene in established drug-induced hyperthermia
    has not been documented from a scientific point of view.  However, the
    effect, as indicated in several case reports (and series of such
    reports), is so convincing that it may be difficult to perform a
    controlled double-blind study due to ethical considerations.

         The prophylactic use of dantrolene prior to anaesthesia in
    susceptible patients may warrant a controlled study.  Due to the
    relatively small number of patients, this should preferably be done
    under a multicenter design.

         In cases of neuroleptic malignant syndrome, a treatment protocol
    using dantrolene versus dantrolene/bromocriptine may be warranted
    (Boles et al., 1982; Goulon et al., 1983).

         The optimum dose regimen of dantrolene is not clearly defined and
    warrants further study.

    4.12.6  Adverse effects

         Dantrolene sodium solution is highly alkaline (pH 9.6) and
    extravasation during intravenous injection may cause tissue necrosis
    (Harrison, 1988).  Due to this risk of severe thrombophlebitis,
    intravenous administration should preferably be given through a
    central venous catheter.  Apart from this, dantrolene appears to be
    well tolerated for the short-term use discussed in this monograph
    (Kolb et al., 1982, Shime et al., 1988).

         Several side effects have been reported in patients receiving
    chronic dantrolene treatment for spasticity.  Muscular weakness,
    drowsiness, dizziness and general malaise commonly occur and
    gastrointestinal disturbances are seen less frequently.  Rare adverse
    effects have included hallucinations (Andrews et al., 1975),
    exacerbation of respiratory depression (Rivera et al., 1975),
    pleuropericardial reaction (Petusevsky et al., 1979; Miller & Haas
    1984), lymphocytic lymphoma (Wan & Tucker, 1980), and leucopenia
    (Greenspun & Pacho, 1981).  The most serious reaction in long-term use
    is hepatotoxicity.  Hepatotoxicity

         Hepatotoxicity may occur when patients are treated with
    dantrolene, as indicated in a review by Chan (1990).  In general,
    therapy was given for at least two months before injury became
    evident.  In 107 adult cases of dantrolene hepatotoxicity, 40 (37%)
    received 200 mg/day or less; 48 (45%) received up to 400 mg/day, and
    the highest dose given was 1600 mg/day (Chan, 1990).  Biochemical
    abnormalities of liver function were observed in about 1.8% of
    patients being given long-term dantrolene treatment and fatal
    hepatitis occurred in 0.3%.  The risk of hepatic injury was greatest
    in females, in patients receiving doses over 300 mg/day, and in those
    treated for over 60 days (Utili et al., 1977).  The major histological
    pathology was subacute hepatic necrosis or chronic active hepatitis,
    although cholestasis has been reported.  Interaction with calcium antagonists

         The combination of calcium antagonists and dantrolene may result
    in systemic hyperkalaemia and even cardiovascular collapse, and should
    therefore be avoided (Yoganathan, 1988).

    4.12.7  Restrictions for use

         When dantrolene was used prophylactically 5 days before delivery
    to twenty pregnant women, no adverse effect on the fetus or newborn
    infant could be detected (Shime et al., 1988).  A possible teratogenic
    effect could, however, not be ruled out from these data.

         Reconstituted dantrolene should not be used if more than 6 h has
    passed since it was made up or if the solution has not been protected
    from light.

    4.13  Model Information Sheet

         The current theory is that dantrolene relaxes peripheral striated
    muscle by preventing Ca2+ flux across the sarcoplasmic reticulum and
    thereby reducing the free intracellular calcium concentration.  Since
    malignant hyperthermia and other drug-induced hyperthermias are
    considered to be a paroxysmal hypercatabolic reaction of these
    muscles, the hyperpyrexia is counteracted by the effect of dantrolene. 
    When the doses recommended in this monograph are used, dantrolene has
    no significant effect on other calcium-dependent systems.

    4.13.1  Uses as an antidote

         Use of dantrolene is indicated in:

    a)   the treatment of malignant hyperthermia induced in susceptible
         individuals by anaesthetic agents or skeletal muscle relaxants;

    b)   the treatment of malignant neuroleptic syndrome;

    c)   the treatment of hyperpyrexia due to poisoning with strychnine,
         Cicuta species (water hemlock) or phencyclidine, and perhaps also
         hyperpyrexia due to poisoning with amphetamines, cocaine,
         lysergic acid diethylamine (LSD), theophylline or monoamine
         oxidase inhibitors.

         The prophylactic use of dantrolene prior to anaesthesia to
    susceptible patients should be considered controversial and is not
    generally recommended.

    4.13.2  Dosage and route

         Whenever indicated, dantrolene treatment must be started without
    delay. Dantrolene is often ineffective if treatment is delayed for 2
    h after the onset of signs in children, or 6 h after the onset of
    signs in adults.

         In the treatment of severe drug-induced hyperthermia, including
    acute malignant hyperthermia induced by anaesthetic agents, dantrolene
    must be given intravenously as soon as the diagnosis is made.  The
    initial dose is 1-2.5 mg/kg given intravenously (1 mg/kg per min), and
    the effectiveness of the treatment should be monitored closely.  A
    dose of up to 10 mg/kg may be given again every 15 min (1 mg/kg per
    min) if signs and symptoms do not subside.  Doses greater than 10
    mg/kg are rarely needed.

         The recurrence of symptoms should be treated in the same way.  To
    prevent this, dantrolene can be given orally in divided doses at a
    total dosage of 4 mg/kg per day.

         Provided adequate supportive therapy (section 12.3) is given,
    dantrolene treatment can usually be stopped within 2 days in cases of
    malignant hyperthermia. Oral treatment may be given for up to 10-14
    days in cases of malignant neuroleptic syndrome, or even longer if
    depot neuroleptics have precipitated the syndrome.

         In the controversial prophylaxis of malignant hyperthermia in
    susceptible individuals, dantrolene may either be given orally at a
    dosage of 4-8 mg/kg per day for 1 to 2 days prior to anaesthesia, or
    intravenously as a single dose of 2.5 mg/kg 1-2 h prior to
    anaesthesia.  This approach is, however, not generally recommended.

    4.13.3  Precautions and contraindications

         Solutions of dantrolene should be protected from light.

         Solutions of dantrolene are strongly alkaline (pH 9.5). 
    Extravasation may cause tissue necrosis.  The dantrolene solution

    should therefore be injected via a fast-flowing intravenous infusion
    into a large vein, or preferably through a central venous catheter.

         Hepatic failure should be considered as a relative
    contraindication and there should be a firm diagnosis for the use of
    dantrolene is this situation (e.g., no prophylactic use).

    4.13.4  Pharmaceutical incompatibilities and drug interactions

         Dantrolene sodium powder should only be diluted with sterile
    water for injection, and is incompatible with other infusion fluids.

         The combination of dantrolene and calcium antagonists should be
    avoided, as severe hyperkalaemia and myocardial depression may occur. 
    Treatment with calcium antagonists should therefore be discontinued 
    if dantrolene is given or may be given.

    4.13.5  Adverse effects

         The major adverse effect is hepatic toxicity, which may be fatal,
    although this is unlikely in the acute setting discussed here.  Few
    side effects have been reported at the dose levels recommended in this

         In chronic treatment (muscle rigidity), dantrolene may also cause
    muscle weakness, drowsiness, dizziness and malaises.  Hallucinations,
    exacerbation of respiratory depression, pleuroperitonitis, lymphocytic
    lymphoma and leucopenia have been  reported rarely.

         When given intravenously, dantrolene solution is highly irritant. 
    Extravasation may cause tissue necrosis.

    4.13.6  Use in pregnancy and lactation

         There is no evidence that dantrolene is harmful when given
    prophylactically to predisposed mothers before delivery.  No adverse
    effects on the fetus or newborn infant have been reported.  Dantrolene
    crosses the placenta (the fetal:maternal concentration ratio is 0.4:1)
    and is excreted in breast milk.  It would be prudent to avoid breast
    feeding if dantrolene were being taken for prophylaxis or treatment.

    4.13.7  Storage

         Dantrolene powder and capsules are stable at temperatures below
    40 °C.  The capsules should be stored in well-sealed containers. 
    Following reconstitution with sterile water, dantrolene sodium
    injection solution is stable for only 6 h at room temperature. 
    Solutions should be protected from light.

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                                         APPENDIX 1
    List of Antidotes

    Group 1


    Antidote                      Main indication               Other possible
                                  of pathological               applications

    ACETYLCYSTEINE                PARACETAMOL                   ORGANOCHLORINE
                                                                SOLVENTS, AMANITIN

    AMYL NITRITE                  CYANIDE                       HYDROGEN SULFIDE


    ATROPINE                      CHOLINERGIC SYNDROME

    ACID (ATA)



    CALCIUM CHLORIDE OR           HF, FLUORIDES,                CALCIUM
    OTHER CALCIUM SALTS           OXALATES                      ANTAGONISTS

    DANTROLENE                    MALIGNANT                     MALIGNANT NEUROLEPTIC
                                  HYPERTHERMIA                  SYNDROME

    DEFEROXAMINE                  IRON, ALUMINIUM               PARAQUAT


    Antidote                      Main indication               Other possible
                                  of pathological               applications

    DIAZEPAM                      CHLOROQUINE



    DIMERCAPROL                   ARSENIC                       COPPER, GOLD, MERCURY
                                                                (INORGANIC), LEAD


    ETHANOL                       METHANOL, ETHYLENE            ALKOXYSILANES
                                  GLYCOL, GLYCOL ETHERS



    GLUCAGON                      BETA-BLOCKERS

    GLUCOSE                       INSULIN

    GUANIDINE                     BOTULISM



    Antidote                      Main indication               Other possible
                                  of pathological               applications


    METHIONINE                    PARACETAMOL




    NALOXONE                      OPIATES

                                  (CURARE TYPE) PERIPHERAL

    OXIMES                        ORGANOPHOSPHATES

    OXYGEN                        CYANIDE, CARBON MONOXIDE,
                                  HYDROGEN SULFIDE

                                                                SULFIDE, CARBON


    Antidote                      Main indication               Other possible
                                  of pathological               applications

    PENICILLAMINE                 COPPER                        GOLD, LEAD,



                                  SYNDROME FROM ATROPINE        SYNDROME FROM
                                  & DERIVATIVES                 OTHER DRUGS


    (PRUSSIAN BLUE C177520)

    PRENALTEROL                   BETA-BLOCKERS



    PYRIDOXINE                    ISONIAZID                     ETHYLENE GLYCOL,


    Antidote                      Main indication               Other possible
                                  of pathological               applications

    SILIBININ                     AMANITINE

    SODIUM NITRITE                CYANIDE                       HYDROGEN SULFIDE



    SODIUM THIOSULFATE            CYANIDE                       BROMATE, CHLORATE,

    SUCCIMER (DMSA)               LEAD, MERCURY

    TOCOPHEROL                    CARBON MONOXIDE               OXYGEN TOXICITY



    UNITHIOL (DMPS)               ARSENIC                       COPPER, NICKEL,
                                                                LEAD, CADMIUM,
                                                                MERCURY (METHYL
                                                                AND INORGANIC)
    Group 2

     Agents used to prevent the absorption of poisons,
     to enhance their elimination or to treat
     symptomatically their effects on body functions

    A.    Emetics


    B.    Cathartics and solutions used for whole gut lavage


    C.    Agents to modify urinary pH


    D.    Agents to prevent absorption of toxic substances in the
          gastrointestinal tract

                                            DIGITALIS, COUMARIN, KEPONE

         FULLERS EARTH                      PARAQUAT, DIQUAT, POTASSIUM,
                                            COPPER, FERROCYANIDE

         SIMETHICONE                        FOAMING DETERGENTS

         SODIUM BICARBONATE                 IRON, MERCURY,

         SODIUM SULFATE                     LEAD, BISMUTH, BARIUM

         STARCH                             IODINE

    E.    Agents to prevent absorption and/or damage in the skin


         MACROGOL 400                       PHENOL

    Group 3

     Other useful therapeutic agents for
     the treatment of poisoning

         Below are listed certain therapeutic agents which are not
    antidotes according to the accepted definition, but which through
    their importance and sometimes specific role in the treatment of
    poisonings, border on the concept of "antidotes".

         In practice, these agents are used very often in cases of
    poisoning and in other medical circumstances.  The usefulness of these
    agents is in general well established, most of them are considered
    essential drugs, and they should be available for immediate use.


    Agents                          Indications - symptoms arising from poisoning


    BENZTROPINE                     dystonia

    CHLORPROMAZINE                  hallucinatory and psychotics states

    CORTICOSTEROIDS                 acute allergic reactions, largyngeal oedema,

    DIAZEPAM                        convulsions, excitation, anxiety, muscular

    DIPHENHYDRAMINE                 dystonia

    DOBUTAMINE                      myocardial depression

    DOPAMINE                        myocardial depression, vascular relaxation

    EPINEPHRINE (ADRENALINE)        anaphylactic shock, cardiac arrest

    FUROSEMIDE                      fluid retention, left ventricular failure

    GLUCOSE                         hypoglycaemia

    HALOPERIDOL                     hallucinatory and psychotic states

    HEPARIN                         hypercoagulability states

    LIDOCAINE                       ventricular arrhythmias

    MANNITOL (IV)                   cerebral oedema, fluid retention


    Agents                          Indications - symptoms arising from poisoning


    OXYGEN                          hypoxia

    PANCURONIUM                     muscular rigidity, convulsions

    PROMETHAZINE                    allergic reactions

    SALBUTAMOL                      bronchoconstriction (systemic/inhaled)

    SODIUM BICARBONATE              acidosis, some cardiac disturbances (e.g.,
                                    TCA poisonings)
    Group 4

     Antidotes and related agents considered obsolete


    Antidote                        Indicated for


    ASCORBIC ACID                   Methaemoglobinaemia

    CYCLOPHOSPHAMIDE                Gold-Paraquat

    CYSTEAMINE                      Paracetamol


    FRUCTOSE                        Ethanol

    LEVALLORPHAN                    Opiates

    NALORPHINE                      Opiates

    POTASSIUM PERMANGANATE          Fluorides

    SULFADILIDINE                   Amanitine

    TANNINS                         Alkaloids

    THIOCTIC ACID                   Amanitine

    TOCOPHEROL (Vitamin E)          Paraquat

    UNIVERSAL ANTIDOTE              Ingested poisons

    COPPER SULFATE                  as an emetic

    SODIUM CHLORIDE                 as an emetic

    CASTOR OIL                      as a cathartic

    ACETAZOLAMIDE                   as a urinary pH modifier



         For many antidotes, the data on both efficacy and the optimum
    methods of use are inadequate.  Furthermore, there are problems in
    both the pre-clinical and clinical aspects of antidote use, as well as
    variations in licensing requirements between different countries. 
    Consequently, the IPCS and the CEC decided to evaluate antidotes and
    other agents used in the treatment of poisoning cases.  For this
    purpose, a methodology has been developed for evaluation of antidotes
    based on the principles concerned with the pharmaceutical properties
    of the substance, its toxicity, as derived from animal and other
    experiments, and the clinical studies in man, which demonstrate its
    efficacy as an antidote and its safety in clinical use.  All aspects
    of these principles, as described below, may not be applicable to each
    antidote and agent, but they provide the basis for assessment of those
    in current use and under development.

    1.  Pharmaceutical Properties

         As is true of any material to be administered to man, clear
    guidelines on the pharmaceutical properties of an antidote are
    required (reference should be made to the criteria as formulated in
    generally accepted National or Regional Pharmacopoeias).  The
    information on an antidote should, therefore, include its chemical
    formula and physical properties, such as melting point, solubility in
    appropriate vehicles for administration, optical properties, acidity,
    stability in light, and thermal stability.  Particular account must be
    taken of the wide range of temperatures to which such compounds may be
    exposed in clinical situations (-30 to +40 °C).  For liquids, the
    refractive index and specific gravity should be considered, and, for
    solids, their loss of weight on drying may be important.

         To ensure purity and uniformity of the antidote preparation, the
    route of synthesis, manufacturing process, and excipients need to be
    considered and may have to be specified.  Similarly, analytical
    methods for the quality control or identification of the antidote
    should be established.

         Storage requirements and limitations need to be considered and
    the shelf-life is very important for compounds that may be held for
    long periods, particularly under tropical conditions.  Evaluations of
    shelf-life will need to be revised as further information on the
    effects of storage under various conditions becomes available. 
    Mention should be made of any incompatibility with other
    pharmaceuticals or food.

    2.  Pre-clinical Studies

         Pre-clinical studies include those undertaken  in vitro, in
    laboratory animals, and in man (human volunteer studies).  In the case
    of antidotes, unlike other pharmaceutical products, studies of this
    nature may first be indicated following the clinical use of postulated
    antidotes or as part of a re-evaluation procedure, in particular where
    comparison of the efficacy of antidotes is indicated.

    2.1  In vitro studies

         The type of  in vitro study will vary depending on the antidote
    being evaluated.  Standardized studies of properties such as
    adsorption capacity, chelating activity, anticaustic activity,
    neutralization (e.g., for acids or alkalis), biochemical actions, and
    pharmacological properties may be appropriate for the range of
    different kinds of antidote.

         Isolated cell, tissue culture, and isolated organ techniques may
    be particularly relevant and  in vitro studies should enable
    subsequent studies in animals and man to be targeted more

    2.2  In vivo studies

    2.2.1  Pharmacodynamic studies

         Pharmacodynamic studies are aimed at assessing the mode of action
    and efficacy of an antidote and its use in any particular type of
    poisoning.  Studies should be performed in relevant animal species and
    should include investigations of both the pharmacological activity of
    the antidote alone and the efficacy against the toxic agent when this
    is administered in appropriate dosages.  Ideally studies should be
    conducted on two unrelated species that show qualitatively similar
    response to the toxin in humans, and the efficacy against two
    appropriate doses of the toxic agent (moderate and high toxicity)
    should be evaluated.  If animals are anaesthetized for such studies,
    then it is important that consideration be given to the effects of any
    anaesthetic agent, and, ideally, two different types of anaesthetic
    should be used in parallel experiments.

         The toxic compound should be administered by a clinically
    relevant route and, if possible, a dose-response relationship for the
    antidote established.  Opportunity should be taken to study the
    pharmacokinetics of the toxic agent and antidote during these studies,
    particularly examining interactions in the distribution and clearance
    of antidote and toxic compound.

    2.2.2  Kinetic studies

         Studies of the absorption, distribution, and elimination of an
    antidote should, where possible, include monitoring of its metabolism
    and also include a study of the effects of dose on its kinetics. 
    Doses used should be relevant to the likely clinical situation. 
    Kinetic studies should take into account the likely route of use of
    the antidote (e.g., oral, parenteral, or topical) and should, ideally,
    include the effect of the antidote on the kinetics of the toxic
    substance against which it is used.  Studies on the influence of
    single or multiple organ failure on the elimination and metabolism of
    the antidote or antidote complex may also be relevant.

    2.2.3  Toxicological studies

         Ideally, toxicological studies should be performed on species
    that show similarity to humans as regards the kinetics and metabolism
    of the antidote.  Acute toxicological studies on two (unrelated)
    species would be appropriate.  The extent of toxicity evaluation would
    depend on the proposed use of the antidote, and, for the situations in
    which repeated doses of an antidote are necessary, chronic toxicity
    studies need to be undertaken.  Consideration should also be given to
    the general approach to acute toxicity studies, bearing in mind the
    doubts about the usefulness of LD50 values.  Depending on likely
    use, teratogenicity, mutagenicity, and carcinogenicity testing may be
    deemed necessary.

    2.3  Human volunteer studies

         Human volunteer studies with antidotes present specific problems
    and should be carried out in accordance with the Declaration of
    Helsinki and the Council for the International Organizations of
    Medical Sciences (CIOMS) Proposed International Guidelines for
    Biomedical Research involving Human Subjectsa.  The ethical
    implications require particular attention.  However, volunteer studies
    may be important and useful for evaluating the human pharmacology of
    certain antidotes.  On special occasions, it may also be possible to
    study interaction with a potentially toxic substance in volunteers,
    subject to full and appropriate ethical review.  Such investigations
    may be particularly relevant for antidotes that are likely to be
    widely used.  They may also aid in choosing the appropriate dosage
    regimen of an antidote for clinical use.  In some circumstances
    studies on patients with a particular disease or of particular age
    groups may be indicated (e.g., renal, cardiac, or hepatic impairment,
    and the elderly).  In the rare situation in which pharmacogenetic
    differences due to polymorphism of metabolism of the antidote is
    important, such human volunteer studies will obviously be valuable.
    a  Proposed International Guidelines for Biomedical research
       Involving human Subjects, 1982, Geneva, World Health

    3.  Clinical Studies

         By their very nature, poisonings of whatever sort are
    unpredictable, and it is often difficult to establish the exact dose
    of toxic compound to which a patient has been exposed.  Clinical
    studies of antidotes are therefore inherently more difficult than
    studies of the effects of pharmaceutical preparations in many other
    conditions, since definition of the severity of the poisoning is often
    a problem.

         The precise combination of approaches used in clinical studies of
    an individual antidote needs to be carefully tailored.  More than one
    antidote may sometimes be needed, and, in these circumstances, an
    evaluation of the combined treatment approach should be given.

    3.1  Literature evaluation

         Published work on antidotes is frequently in the form of case
    reports, which are by their nature uncontrolled.  Such studies are an
    important source of data and can provide information on both the
    effect of an antidote in the clinical setting and the likely pattern
    of toxicity associated with the poison.  They may thus prevent
    needless duplication of studies.  A principal role for a continued
    evaluation of the literature is to identify specific areas for future
    work and areas of ignorance.

         Case reports are often not well documented and it is rarely
    possible to make strict comparisons between published cases undertaken
    at different centres.  The human toxicological scientific basis could
    be greatly enhanced by the establishment of a comparable basis for
    case data collection and reporting (see below).

    3.2  General approach to clinical studies

         Double-blind controlled studies are the ideal in most areas of
    therapeutics.  In the assessment of antidotes, however, particularly
    for rarer poisonings and those with a high morbidity or mortality,
    such an approach presents major ethical and technical problems.  Thus,
    it may not be possible to obtain the consent of the patient or his
    relatives and an individual clinician is unlikely to see a sufficient
    number of patients to make a formal study worthwhile. The proper
    construction of a control group may also raise ethical dilemmas. 
    Thus, a prospective approach to the study of antidotes should be
    considered in parallel with the critical retrospective analysis of
    existing patient data.  Such studies may be best carried out on a
    multi-centre or multi-national basis.  This retrospective analysis,
    often of unpublished data, could perhaps be organized centrally. 
    Retrospective data will provide a useful baseline from which to mount
    prospective studies.

    3.3  Methodology

         Since case records are a major data source in antidote studies,
    it is essential that records are kept carefully in a standardized
    format.  Case records should, where possible, include a detailed
    personal history to cover occupational exposure, toxic agents,
    relevant hobbies, previous medical history, and concurrent medication
    including non-prescribed medicines.  Physical examination should pay
    particular attention to specific signs of intoxication and their
    physiological consequences.  Careful measurement and monitoring of
    physiological changes is essential; in particular, careful
    documentation of changes, such as the level of consciousness, should
    be established.  A scoring system for monitoring changes in the level
    of consciousness and an agreed coma scale for grouping patients into
    classes of comparable severity should be adopted where possible. 
    Detailed consecutive records of clinical progress in an individual
    patient are important.  Accurate recording of the time of the
    intoxication, of its presentation to treatment centres, and of
    initiation of treatment are particularly important.

         The clinical examination should be supported by appropriate
    analytical data on samples of body fluid such as blood, urine, and
    gastric aspirate.  The collection, handling, and analysis of samples
    needs to be standardized and guidelines for individual toxic compounds
    laid down.  Accurate records of the time of clinical examination and
    toxicological sampling are necessary and, where possible, the two
    should be concurrent and continue throughout the clinical course of
    the poisoning.  This may enable a relationship between the two to be
    established, as well as providing careful documentation of the effect
    of an antidote.  The routine saving of multiple biological samples
    from a patient suffering from intoxication is therefore necessary.

         It should be stressed that objective measures are preferable to
    clinical impressions and that the opportunity should be taken at all
    stages of management of intoxications to quantify physiological
    parameters.  Where possible, accepted standardized prognostic factors
    should be utilized both to determine the appropriate use of the
    antidote and to evaluate its effect.

    3.4  Controlled studies

         In the past, controlled studies have provided the basis for
    important advances in the management of poisonings.  As indicated in
    section 3.2, there are ethical consideration that need to be
    considered carefully.  Furthermore, such studies need to be carefully
    tailored to the particular antidote and poison under investigation. 
    The general poisons made in section 3.3 will also apply.

         Careful consideration needs to be given to the establishment of
    a control group.  This should ideally be a parallel and comparable
    group of patients but may be retrospective.  Establishment of a
    parallel control group may be easier in the situation where two active
    treatments are being compared.  It should be remembered, however, that
    there may be a risk attached to using an antidote, and the use of a
    control group that receives full supportive therapy may enable a more
    rapid decision on the efficacy of an antidote to be obtained.

         In controlled studies, an opportunity may arise to study the
    toxicity and kinetics of the antidote; it should be grasped whenever

         The period of follow-up needs to be determined, and end-points
    must be clearly established and defined.  Statistical considerations
    are important and need to be fully incorporated at the time of trial

    4.  Centralized Record System

         It is suggested that a central pooling of the experience of
    various treatment centres, particularly with respect to rarer
    antidotes, would be a great advantage.  An international network of
    IPCS-designed clinical centres could provide a mechanism for this
    purpose.  This pool of data would be used as a basis for the
    international evaluation of antidotes but would remain confidential
    and would not be published without the consent of the individual
    clinician concerned.  Data submitted to such a pool would remain the
    property of the investigator, who would be at liberty to publish it

         Poison control centres appear to be in a unique position to
    collect data on antidotes for rarer poisoning and to ensure that
    appropriate clinical and toxicological data are collected.  This
    process might be facilitated if a poison control centre acted as a
    base for the supply of antidotes.

         The amount of information required from individual patients
    entered on the case record system would have to be carefully planned
    and the collection and reporting of the data coordinated.

         The establishment of such a centralized case record system would
    also be likely to stimulate further international collaboration in the
    evaluation of antidotes by controlled studies and could lead to
    recommendations for further areas of research.



    Guidelines to Authors

         These guidelines provide a unified format for monographs written
    on individual antidotes used in the management of poisoning using
    existing published (and unpublished) literature.  For a number of
    antidotes currently used clinically some of the information suggested
    will be missing: these gaps in knowledge should be stated.  For those
    antidotes currently under in development, this proforma is designed to
    give an idea of the sort of information that would be required for
    evaluation and worldwide acceptance for use. Suggested section
    headings and an outline guide to contents are given below.

    1.  Introduction

    This should be brief (usually 200-400 words) and include:

    -    indications for antidote use
    -    rationale for the choice of the antidote, mentioning areas where
         there are doubts about efficacy
    -    an indication of specific groups at risk from treatment with the

    2.  Name and Chemical Formula of Antidote

         International non-proprietary name (when available); CAS number
    (Chemical Abstracts Service); IUPAC name (International Union of Pure
    and Applied Chemistry); manufacturer and commercial names, formula
    (include figure of structure); relative molecular mass; specification
    of chemical salts used; conversion table from mass units to SI units.

    3.  Physico-chemical Properties

    -    melting point, boiling point
    -    solubility in vehicles for administrations
    -    optical properties
    -    acidity
    -    pKa
    -    stability in light
    -    thermal stability/flammability (including vehicle if antidote
         usually in solution or suspension)
    -    for liquids, refractive index and specific gravity
    -    for solids, loss of weight on drying
    -    the excipients and pharmaceutical aids
    -    pharmaceutical incompatibilities

    4.  Pharmaceutical Formulation and Synthesis

         4.1    Routes of synthesis (brief details only)
         4.2    Manufacturing processes (indicate, where known, possible
         4.3    Presentation and formulation

    5.  Analytical Methods

         In this section, the passive voice should be used, e.g., "the
    solution is mixed to dissolve the reagents".  Vocative instructions
    should  not be used, e.g., "dissolve 0.5 g in 20 ml of water".  To

         5.1    Quality control procedures for the antidote and/or its
         5.2    Methods for identification of the antidote
         5.3    Methods for analysis of the antidote in biological samples
         5.4    Analysis of the toxic agent in biological samples
                referring to the preferred assay techniques

    6.  Shelf-life

         Attention should be given to specific conditions of temperature
    and humidity, including tropical conditions, and instructions on
    storage conditions.

    7.  General Properties

         This section should be particularly tailored to the antidote in
    question and include:

    -    information on the mode of antidotal activity of the compound
         (e.g., chelating agent, receptor antagonist)
    -    other relevant biochemical and pharmacological profiles (e.g.,
         anticholinergic, antiadrenergic properties) as demonstrated  in
          vivo and  in vitro

         This section can be subdivided as needed.

    8.  Animal Studies

         It is important to exclude human data from this section.  Even if
    a paper presents both human and animal data, the human data should be
    given in the clinical sections 9, 10 or 11, as appropriate.  An
    attempt should be made to evaluate the statistical significance of the
    results.  As a rule of thumb, this term should imply a level of
    statistical significance at the 5% level (P <0.05).  If other
    parameters are used, they should be given.  If both positive and
    negative results have been reported, possible reasons for such

    differences may be briefly discussed (routes of administration, time
    before giving the antidote, dose, etc.).

    8.1  Pharmacodynamics

         This section should include data on efficacy, examining the
    protective effects against moderate and high doses of the toxin.  The
    efficacy parameter end-point should be defined before the data are
    discussed, e.g., is it reduced mortality or increased excretion of the
    toxic agent that has been studied?  Data on the dose-response
    relationship of the antidote and on the pharmacokinetics of any
    interaction between antidote and toxic compound should be sought. Both
    the toxic agent and the antidote should be given by the clinically
    relevant route(s). Information should also be sought on the time after
    the administration of the toxic agent at which the antidote is likely
    to be of any clinical benefit.

    8.2  Pharmacokinetics

         Studies on the bioavailability, half-life and clearance of the
    antidote by the relevant route of administration; studies on the dose
    dependency of the pharmacokinetics relevant to the doses used in the
    clinical settings and details of the metabolism of the compound.  If
    there are data on more than one species, these should be included.

    8.3  Toxicology

         Details of acute, subacute or chronic toxicity, depending on the
    likely clinical use of the compound, should be discussed.  Such
    studies should use appropriate routes of administration.  Where
    available, details of mutagenicity and teratogenicity testing would be
    of interest.  LD50 values for different species and different routes
    of administration should be presented.

    9.  Volunteer Studies

         Information on the pharmacokinetics of the antidote in man and
    possible effects of disease on the handling of the antidote should be
    given, where available.  Studies on the interaction with the toxic
    agent given at subtoxic doses may also be available.  All human data
    based on volunteer studies should be included in this section.

    10.  Clinical Studies - Clinical Trials

         Literature evaluation of clinical trials.  For each trial the
    following information should be given:

    (a)  evidence of poisoning, i.e. inclusion criteria

         (i)    definition of assay techniques to measure the poison and
                its effects
         (ii)   physiological changes of poisoning recorded; accepted

    (b)  number of patients studied

    (c)  was there a control group?  type, i.e. parallel or retrospective;
         appropriate, i.e.   were the treated and control groups
         comparable (e.g., age, sex, time of   presentation, severity of

    (d)  details of antidote used

         (i)    dose and route
         (ii)   time between exposure to the toxin and administration of
         (iii)  evidence of any toxic effect of the antidote

    (e)  outcome assessment

         (i)    clinical
         (ii)   biochemical
         (iii)  end-points - death, pathological damage

    (f)  overall view of likelihood of benefit due to antidote

         It may sometimes be difficult to define what is a clinical trial.
    Retrospective studies and use of historical controls should normally
    not be considered as clinical trials and may then be described under
    section 11.

    11.  Clinical Studies - Case Reports

         Many authors of case reports claim a favourable outcome "due to
    the use of the antidote".  In most cases, however, the best conclusion
    drawn from such studies is that the use of the antidote was associated
    with a favourable outcome and nothing more.  Some case reports are
    thoroughly performed with measurement of half-lives in different body
    compartments and amount of toxic agent eliminated by different
    elimination techniques.  When referring to such studies, the end-point
    parameter, e.g., reduction in plasma half-life, should be evaluated

    critically.  There may be too few plasma levels over a too short a
    time period to allow for any conclusion.

    Other important items to evaluate are:

    -    evidence of poisoning (clinical, pathological);
    -    was an appropriate assay/measurement technique used?
    -    dose and route of antidote
    -    evidence of outcome
    -    evidence of toxicity or side-effects of antidote

         It should be borne in mind that most poisoned patients will
    recover with intensive supportive care alone.  If such cases have been
    reported, a brief mention may be appropriate.

    12.  Summary of Evaluation

         This section is frequently misunderstood by authors writing their
    first draft in this series.  Section 12 is not to be a copy of section
    13.  In section 12 the author should try to  evaluate or summarize
    the data, previously presented in the monograph, as a basis for the
    recommendations under the following subheadings:

         12.1   Indications
         12.2   Advised routes and dose
         12.3   Other consequential or supportive therapy
         12.4   Controversial issues and areas of use where there is
                insufficient information to make recommendations
         12.5   Proposals for further studies
         12.6   Adverse effects
         12.7   Restrictions for use

    13.  Model Information Sheet

         This should be a concise user's manual for this antidote in the
    emergency situation.  This section may, for example, be faxed to the
    clinician treating the patient.  No references or abbreviations should
    be given since all the information given should have been discussed in
    previous sections.

         13.1   Uses
         13.2   Dosage and route
         13.3   Precautions/contraindications
         13.4   Pharmaceutical incompatibilities and drug interactions
         13.5   Adverse effects
         13.6   Use in pregnancy and lactation
         13.7   Storage

    14.  References

         References should be given in text as (McMartin et al., 1980) or
    (Henry & Volans, 1984).  Several references to the same statement are
    placed in chronological order.

         In the reference list, the names of all authors and their
    initials must be given.  Only initial letters are capitalized.  Titles
    of articles in languages other than English, except those in French,
    should be translated into English.  Translated titles appear in square
    brackets with the original language in parentheses.


         Names of journals should be abbreviated according to the ISDS
    (International Serials Data System) List of Serial Title Word
    Abbreviations (a condensed list is obtainable from the RO) or
    otherwise given in full.  The initial letter of each abbreviation is
    capitalized.  The volume number is indicated in bold print and is
    followed by the issue number (if any) in parentheses.  First and last
    page numbers must be given.

    McMartin KE, Ambre JJ & Tephly TR (1980)  Methanol poisoning in human
    subjects. Am J Med, 68: 414-418.

    Henry J & Volans G (1984)  ABC of poisoning.  Br Med J, 289: 990-993.

     Conference proceedings

         The following elements are necessary: name(s) and initial(s) of
    author(s); the year of publication; title of paper; the word "In:" the
    editors of the proceedings; the full title of the conference (not
    abbreviated); the place and date of the conference; the place of
    publication; the publisher; the volume number (if any) and the page


         Wassermann M (1984) L'étude de la toxicologie des pesticides en
         climat tropical In: Smith JH ed. Proceedings of the 14th
         International Congress of Occupational Health, Madrid, 16-21 May
         1983. Amsterdam, Excerpta Medica, vol 3, 1728-1733.


         Windholz M ed. (1983) The Merck Index: an encyclopedia of
    chemicals, drugs, and biologicals, 10th ed. Rahway, New Jersey, Merck
    and Co., Inc.

         Reference to a chapter in a book should be given as follows:

         Weinstein L (1974) Pathogenic properties of invading
         microorganisms. In:  Sodeman WA Jr ed. Pathologic physiology:
         mechanisms of disease. New York, Academic Press, pp 457-472.

     Agency report

         US EPA (1984) Mercury health effects update: health issue
    assessment.  Washington, DC, US Environmental Protection Agency

     Order of entries in the list

         The following rules are applied:

         a)   Several papers by different authors with the same surname
              are listed alphabetically according to their initials.

         b)   Several papers by one author are listed chronologically.

         c)   Several papers by the author plus a co-author are listed

         d)   Several papers by the author plus two or more coauthors are
              listed chronologically.


         Smith DE (1985)
         Smith JH (1983)
         Smith JH (1984)
         Smith JH & Barns MP (1986)
         Smith JH & Jones TD (1979)
         Smith JH, Jones TD, & Barnes MP (1981)
         Smith JH, Barnes MP, & Jones TD (1983)

         Normally one should not refer to abstracts or works published as
    supplements. Under special circumstances, e.g., little has been
    published and the person has great experience with the topic, personal
    communications may be inserted in the text as follows: (Vale JA,
    personal communication).

    15.  Author(s) Name, Address

    16.  Additional Information
         e.g., availability of supply.

    See Also:
       Toxicological Abbreviations