Formulary
Prazosin: Indications, Dosing, Side Effects and Interactions
Prazosin clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 4 min read
Prazosin: Indications, Dosing, Side Effects and Interactions
Prazosin clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Hypertension**
- **Adult** (By Mouth): Initially 500 micrograms 2-3 times a day for 3-7 days, the initial dose should be taken on retiring to bed at night to avoid collapse, increased to 1 mg 2-3 times a day for a further 3-7 days, then increased if necessary up to 20 mg daily in divided doses.
**Congestive heart failure (rarely used)**
- **Adult** (By Mouth): 500 micrograms 2-4 times a day, initial dose to be taken at bedtime, then increased to 4 mg daily in divided doses; maintenance 4-20 mg daily in divided doses.
**Raynaud's syndrome (but efficacy not established)**
- **Adult** (By Mouth): Initially 500 micrograms twice daily, initial dose to be taken at bedtime, dose may be increased after 3-7 days, then increased if necessary to 1-2 mg twice daily.
**Benign prostatic hyperplasia**
- **Adult** (By Mouth): Initially 500 micrograms twice daily for 3-7 days, subsequent doses should be adjusted according to response, maintenance 2 mg twice daily, initiate with lowest possible dose in elderly patients.
**Hypertension for prazosin**
- **Child 1 month-11 years** (By mouth): Initially 10-15 micrograms/kg 2-4 times a day, initial dose to be taken at bedtime, then increased to 500 micrograms/kg daily in divided doses, dose to be increased gradually; maximum 20 mg per day.
- **Child 12-17 years** (By mouth): Initially 500 micrograms 2-3 times a day for 3-7 days, initial dose to be taken at bedtime, then increased to 1 mg 2-3 times a day for a further 3-7 days, then increased if necessary up to 20 mg daily in divided doses, dose should be increased gradually.
**Congestive heart failure (rarely used) for prazosin**
- **Child 1 month-11 years** (By mouth): 5 micrograms/kg twice daily, initial dose to be taken at bedtime, then increased to 100 micrograms/kg daily in divided doses, doses should be increased gradually.
- **Child 12-17 years** (By mouth): 500 micrograms 2-4 times a day, initial dose to be taken at bedtime, then increased to 4 mg daily in divided doses; maintenance 4-20 mg daily in divided doses.
Cautions
Cataract surgery (risk of intra-operative floppy iris syndrome); elderly; first dose hypotension Cautions, further information Elderly For alpha 1 -selective adrenoceptor blockers, Screening Tool of Older Persons' potentially inappropriate Prescriptions (STOPP) criteria to aid medication reviews (see Prescribing in the elderly for information). Potentially inappropriate: in those with symptomatic postural hypotension or micturition syncope (risk of precipitating recurrent syncope) in those with persistent postural hypotension i.e. recurrent drop in systolic blood pressure 20 mmHg (risk of syncope and falls).
Contraindications
History of micturition syncope (in patients with benign prostatic hyperplasia); history of postural hypotension; not recommended for congestive heart failure due to mechanical obstruction (e.g. aortic stenosis)
Side effects
Common or very common Asthenia; constipation; depression; diarrhoea; dizziness; drowsiness; dry mouth; dyspnoea; headache; nasal congestion; nausea; nervousness; oedema; palpitations; postural hypotension; sexual dysfunction; skin reactions; syncope; urinary disorders; vertigo; vision blurred; vomiting Uncommon Angina pectoris; arrhythmias; arthralgia; epistaxis; eye pain; eye redness; gastrointestinal discomfort; hyperhidrosis; paraesthesia; sleep disorders; tinnitus Rare or very rare Alopecia; fever; flushing; gynaecomastia; hallucination; hepatic function abnormal; pain; pancreatitis; vasculitis
Interactions
**Other interactions (10):**
- The anti-hypertensive effect of felodipine may be enhanced by other anti-hypertensive such as alpha-blockers (e.g.
- These include propranolol, prazosin, and numerous others.
- Combinations requiring caution Combinations which can increase the effects of digoxin when co-administered: amiodarone, canagliflozin, daclatasvir, flibanserin, flecainide, prazosin, propafenone,...
- Antihypertensives : Diuretics may enhance the hypotensive action of other hypotension producing medications, including angiotensin-converting enzyme (ACE) inhibitors (enhanced first-dose...
- Alpha-adrenergic antagonists As with other specific -adrenergic agonists, the effect of midodrine is blocked by -adrenergic antagonists such as prazosin and phentolamine.
- Alpha-1-blockers (e.g., prazosin, alfuzosine) When alpha-1-blockers are combined with eplerenone, there is the potential for increased hypotensive effect and/or postural hypotension.
Pregnancy
No evidence of teratogenicity; manufacturers advise use only when potential benefit outweighs risk.
Breast feeding
Present in milk, amount probably too small to be harmful; manufacturer advises use with caution.
Hepatic impairment
Manufacturer advises caution (no information available). Dose adjustments Manufacturer advises initial dose reduction to 500 micrograms daily; increased with caution.
Renal impairment
Dose adjustments Manufacturer advises initial dose reduction to 500 micrograms daily in moderate to severe impairment; increase with caution.
Medicinal forms
Tablet
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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