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    AZAPERONE

    First draft prepared by 
    Dr G. Roberts
    Toxicology Evaluation Section
    Commonwealth Department of Human Services and Health
    Canberra, Australia

    1.  EXPLANATION

           Azaperone is a butyrophenone neuroleptic tranquillizer which had
    been previously evaluated at the thirty-eighth meeting of the
    Committee (Annex 1, reference 97).  At that time, an ADI was not
    established and the Committee requested the following information
    before reviewing the compound again:

    1.     Additional data from genotoxicity studies, which should include:

           (a)    A study with  Salmonella typhimurium strains that were
                  reported by one laboratory to be sensitive to azaperone and
                  some of its metabolites, and

           (b)    studies with cultured mammalian cells in which a variety of
                  effects are investigated, including chromosomal aberrations
                  and the induction of mutations.

           The results of these studies would determine whether further data
           are required.

    2.     Studies from which a NOEL for pharmacological effects in humans
           could be derived.

    3.     A justification for the protocol utilized in the reproduction
           study in rats that was submitted, and in particular for the very
           limited dosing regimen used in the females and the failure to
           dose the males.

    4.     Studies on the concentrations of residues of azaperone and
           azaperol in both muscle and fat of pigs treated with azaperone
           over a 3-day period.

           This monograph addendum summarizes the data that have become
    available since the previous evaluation (Annex 1, reference 98).

    2.  BIOLOGICAL DATA

    2.1  Toxicological studies

    2.1.1  Special studies on genotoxicity

           The results of an  in vitro study of azaperone is summarized in
    Table 1.

        Table 1.  Result of a genotoxicity study on azaperone

                                                                             
    Test system    Test object   Concentration     Results     Reference
                                                                             

    Forward        Mouse         33-237 g/ml1     Negative    van de Waar & 
    mutation       lymphoma      18-100 g/ml2                 Enninga, 1993
                   (L5178Y 
                   TK +/-)
                                                                             

    1    Without exogenous metabolic activation.
    2    With exogenous metabolic activation 
         (aroclor 1254-induced rat liver microsomes).
    
           In two independent experiments, azaperone did not induce forward
    mutations;  appropriate positive control substances gave the expected
    responses, demonstrating the sensitivity of the assay (van de Waart &
    Enninga, 1993).

    3.  COMMENTS

           The information provided included data from a recent genotoxicity
    assay and an evaluation report that discussed all toxicological and
    pharmacodynamic data considered to be relevant to the establishment of
    an ADI for azaperone.

           The Evaluation Report (Van Cauteren  et al. , 1994) states that
    azaperone should not be considered carcinogenic because it is not
    genotoxic, it is not structurally similar to known carcinogens, and no
    unexpected adverse effects were demonstrated in the toxicity studies. 
    Evidence in support of a negative structure-activity relationship
    between azaperone and known carcinogens was not available.  The
    Committee considered that such information should be provided.

           The Committee reconsidered the results from the previously
    reviewed genotoxicity assays.  Conflicting results were reported in
    two studies of azaperone in the  Salmonella typhimurium mutation
    assay.  In one study, positive results were obtained with azaperone
    and some of its synthesized metabolites in the presence of an
    exogenous metabolic activation system.  In the second and more
    thorough study of azaperone, no mutagenic effect was observed.  The
    metabolites were not tested in this second study.  The mutagenicity of
    azaperone and its metabolites in the  Salmonella assay remains
    unresolved.  A new study on cultured mouse lymphoma cells showed no
    mutagenic effects and micronucleus and dominant lethal tests have
    shown no evidence for genotoxic activity.  The Committee concluded
    that the weight of evidence suggests that azaperone has low potential
    for genetic damage.

           In relation to reproductive toxicity studies, the evaluation
    report stated that no adverse effects were found in the male genital
    tract in rats dosed up to 18 months. For this reason a male fertility
    study was not performed.  Although histological changes were not
    observed in the male reproductive tract, this is only one aspect in
    the assessment of reproductive performance.  Therefore, the Committee
    concluded that male fertility had not been adequately assessed and a
    study to assess reproduction and fertility in males was necessary.

           Details were provided that confirmed the NOEL for sedation in
    humans of 30 g/kg bw.  However, the Committee was unwilling to use
    this study in establishing an ADI because the observations were of a
    subjective nature and the experiment was poorly controlled. 
    Reconsidering the pharmacological data, the NOEL of 630 g/kg bw in a
    sensitive assay in the dog was considered to represent a more
    objective and appropriate measure of the pharmacological activity of
    azaperone.

    4.  EVALUATION

           The Committee considered that the pharmacological effects of
    azaperone were the most relevant for the determination of the ADI. 
    Using the NOEL of 630 g/kg bw for pharmacological activity in dogs
    and a safety factor of 200, a temporary ADI of 0-3 g/kg bw was
    established.

    5.  REFERENCES

    VAN CAUTEREN, H., LAMPO, A., VANPARYS, Ph., MAES, L., ENGELEN, M. &
    VAN LEEMPUT, L. (1994).  Review report on the toxicological,
    pharmacokinetic and pharmacodynamic documentation related to
    azaperone.  Unpublished Report No. V8672 from Janssen Research
    Foundation.  Submitted to WHO by Janssen Pharmaceutica, Beerse,
    Belgium.

    VAN DE WAART, E.J. & ENNINGA, I.C. (1993). Evaluation of the mutagenic
    activity of azaperone in an  in vitro mammalian cell gene mutation
    test with L5178Y mouse lymphoma cells (with independent repeat). 
    Unpublished Report No. 94635 by RCC  Notox.  Submitted to WHO by
    Janssen Pharmaceutica, Beerse, Belgium. 


    See Also:
       Toxicological Abbreviations
       Azaperone (WHO Food Additives Series 29)
       Azaperone (WHO Food Additives Series 41)
       AZAPERONE (JECFA Evaluation)