Summary for UKPID
TERAZOSIN HYDROCHLORIDE
Anne Prince, BSc (Hons) MRPharmS
National Poisons Information Service (Newcastle Centre)
Regional Drug & Therapeutics Centre
Wolfson Building
Claremont Place
Newcastle upon Tyne
NE1 4LP
UK
This monograph has been produced by staff of a National Poisons
Information Service Centre in the United Kingdom. The work was
commissioned and funded by the UK Departments of Health, and was
designed as a source of detailed information for use by poisons
information centres.
Peer review group: Directors of the UK National Poisons Information
Service.
Summary
Brand name
Hytrin, Hytrin BPH
Generic
Terazosin hydrochloride
Chemical group/family
Alpha-adrenoceptor blocker
(BNF category 2.5.4 and 7.4.1)
Reference Number
CAS 63590-64-7 (terazosin)
CAS 63074-08-8 (terazosin hydrochloride)
CAS 70024-40-7 (terazosin hydrochloride dihydrate)
Product licence numbers
Hytrin Hytrin BPH
1mg tablet 0037/0159 0037/0234
2mg tablet 0037/0160 0037/0235
5mg tablet 0037/0161 0037/0236
10mg tablet 0037/0162 0037/0237
Manufacturer/supplier
Abbot Laboratories Limited,
Abbott House,
Norden Road,
Maidenhead,
Berks,
SL6 4XE.
Tel (01628) 773355
Presentation
Tablets 1mg,2mg, 5mg,10mg.
Starter packs -7 x 1mg, 7 x 2mg, 21x2mg
Original packs of 28 tablets for 2mg, 5mg,10mg
Physio-chemical properties1
Chemical structure
(RS)-1-(4-Amino-6,7-dimethoxy-2-quinazolinyl)-4-((tetrahydro-2-
furanyl)carbonyl)piperazine monohydochloride dihydrate.
C19H25N5O4.HCL.2H2O.
Molecular weight 459.9
(anhydrous free base) (387.4)
pKa 7.1
Solubility
in alcohol 1 in 244
in water 1 in 40
Uses
Indications:2
Terazosin is indicated for the treatment of mild to moderate
hypertension in combination with other drugs or as sole therapy. It is
also indicated for the symptomatic treatment of urinary
obstruction caused by benign prostatic hyperplasia (BPH).
Therapeutic Dose2
Hypertension/BPH
Initial dose of 1mg at bedtime. The dose may be doubled at weekly
intervals. The usual maintenance dose is 2-10mg for hypertension and
5-10mg for BPH.
Renal Impairment
No dosage alterations necessary.
Elderly
No dosage alterations necessary.
Precautions2
Caution in patients with a history syncope. Dizziness,
light-headedness or drowsiness may occur with the initial dose, or in
association with missed doses and subsequent reinitiation of therapy.
Patients must be advised to avoid driving or alcohol for approximately
12 hours after the first dose or when the dose is increased. Dizziness,
light-headedness or fainting may occur when standing up quickly from
a lying or sitting position and patients should be advised to lie down
if these symptoms appear, and then to sit for a few minutes to prevent
their recurrence.
Contraindications
Known hypersensitivity to terazosin.
Pregnancy
No teratogenic effects seen in animals. The safety of terazosin has
not been established during pregnancy and therefore it should not be
used unless the potential benefit outweighs the risk.
Breast Feeding
It has not been determined whether terazosin is excreted into breast
milk, but it seems unlikely, on theoretical grounds that significant
amounts will pass into the baby through the breast milk.
Pharmacokinetics1
oral absorption
>95%
presystemic metabolism
<10%
plasma half life
range 8-14 hours
mean 12 hours
Volume of distribution
28 L
Plasma protein binding
90-94%
Total body clearance
80ml.min-1
Renal clearance
10ml.min-1
Metabolism (liver)
60%
Toxicokinetics
No data
Epidemiology of poisoning
No data
Adverse effects4
Dizziness, lack of energy, peripheral oedema, somnolence, blurred
vision, nausea, headache, nasal congestion, postural hypotension.
Interactions
Orthostatic or first dose hypotension may be promoted by concomitant
beta-blockade, calcium channel blockade, sodium depletion secondary to
diuretic administration or other drugs which lower the blood pressure.
Mechanism of action/toxicity
Terazosin is a selective long acting alpha-adrenergic antagonist. The
exact mechanism of therapeutic effect is not known. Relaxation of
peripheral blood vessels appears to be produced mainly by competitive
antagonism of post synaptic alpha-1-adrenoceptors. Toxic effects are
mainly extensions of its known pharmacological activity.
Features of poisoning3
Summary
Severe hypotension and severe tachycardia are the most common effects
following overdose with these agents.
Cardiovascular
Hypotension, tachycardia, palpitations and cardiac arrhythmias may be
noted. Severe hypotension may result in myocardial and cerebral
ischemia. Syncope may occur following 1st dose.
Neurologic
Headache, dizziness and sweating may be noted.
Gastrointestinal
Nausea and vomiting are common.
Management3
Treatment is primarily symptomatic and supportive.
Decontamination
One dose of activated charcoal can be administered to prevent further
absorption if presentation is within 2 hours.
Hypotension
Restoration of blood pressure and normalisation of heart rate may be
accomplished by keeping the patient in a supine position. Administer
I.V. fluids and place in Trendelburg position. If unresponsive to
these measures, administer dopamine or noradrenaline and titrate as
needed to desired response.
Monitor
Check heart rate, blood pressure and obtain an ECG.
Check renal function and maintain urine output.
Elimination Techniques
Dialysis is unlikely to be of benefit because terazosin is highly
protein bound.
Case Data
No case reports of terazosin overdose reported in the literature.
Author
Anne Prince, BSc (Hons) MRPharmS
National Poisons Information Service (Newcastle Centre)
Regional Drug & Therapeutics Centre
Wolfson Building
Claremont Place
Newcastle upon Tyne
NE1 4LP
UK
This monograph was produced by the staff of the Newcastle Centre of
the National Poisons Information Service in the United Kingdom. The
work was commissioned and funded by the UK Departments of Health, and
was designed as a source of detailed information for use by poisons
information centres.
Peer review was undertaken by the Directors of the UK National Poisons
Information Service.
Last updated February 1997
References
1. Dollery C. Therapeutic Drugs (Suppl 2), Churchill Livingstone
1994
2. ABPI. Compendium of Data Sheets and Summaries of Product
Characteristics Datapharm Publications Ltd 1996-1997
3. Micromedex, Inc. Poisindex, Volume 91 Expiry Date:31/3/97
4. S.G.Carruthers. Adverse Effects of Alpha-1-Adrenergic Blocking
Drugs
5. Drug Safety 11 (1):12-20 1994
See Also:
Toxicological Abbreviations