ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Alpha-1 Adrenoceptor Antagonist — Raynaud's Phenomenon / Hypertension Pregnancy: Use with caution — limited data; other agents preferred in pregnancy

Prazosin

Brand names: Hypovase

Adult dose

Dose: 500 micrograms 2–3 times daily initially; maintenance 500 micrograms–2 mg 2–3 times daily
Route: Oral
Frequency: 2–3 times daily
Max: 20 mg/day (hypertension); lower doses used for Raynaud's
First-dose hypotension significant — take first dose at bedtime with caution. Short half-life (2–3 hours) requires multiple daily dosing — main disadvantage vs doxazosin. In Raynaud's: reduces adrenergic-mediated digital vasospasm. Less commonly used now — superseded by longer-acting alpha blockers.

Paediatric dose

Dose: 25–50 micrograms/kg mcg/kg
Route: Oral
Frequency: 2–3 times daily
Max: 400 micrograms/kg/day or 20 mg/day
BNFc: used in specialist settings for hypertension and phaeochromocytoma surgery preparation

Dose adjustments

Renal

Start at lower dose (500 micrograms OD) — increased sensitivity in renal impairment

Hepatic

Use with caution — hepatically metabolised

Paediatric weight-based calculator

BNFc: used in specialist settings for hypertension and phaeochromocytoma surgery preparation

Clinical pearls

  • Prazosin was the first selective alpha-1 blocker — now largely replaced by doxazosin (once-daily) and terazosin in hypertension practice
  • Still used in Raynaud's phenomenon particularly in systemic sclerosis when CCBs are insufficient or not tolerated
  • PTSD (off-label, USA): prazosin used for nightmare suppression — alpha-1 blockade in brain reduces noradrenergic hyperactivation during sleep
  • IFIS risk persists permanently — inform ophthalmologist even if prazosin stopped years previously

Contraindications

  • Congestive heart failure due to mechanical obstruction
  • History of micturition syncope

Side effects

  • First-dose hypotension (severe — faint/loss of consciousness)
  • Dizziness
  • Headache
  • Fatigue
  • Palpitations
  • Urinary incontinence (in women)
  • IFIS (cataract surgery risk)

Interactions

  • PDE5 inhibitors — severe additive hypotension
  • Other antihypertensives — additive
  • Beta-blockers — increased first-dose hypotension risk

Monitoring

  • Blood pressure lying and standing
  • Symptoms of orthostasis

Reference: BNFc; BNF 90; BSR/BHPR Raynaud's Guidelines; MHRA Drug Safety Update (IFIS). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways