Prazosin
Prazosin hydrochloride
Also known as: Minipress · Hypovase · CP-12299-1 · furazosin hydrochloride · prazosini hydrochloridum · Prazosinum · Prazosin hydrochloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceSystemic hypertension (extra-label) — Weight-based dosage
- q8-12h
NA
Governing clinical context (2)
- Systemic hypertension (extra-label):
- ■ This medicine may be given with or without food. If your animal vomits, stops eating, or acts sick after getting prazosin on an empty stomach, give the medicine with food or a small treat to see if this helps. If vomiting continues, contact your veterinarian.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Prazosin is a highly selective alpha-1 adrenergic receptor antagonist (sympatholytic).
While historically utilized as a balanced vasodilator (reducing both preload and afterload) for the adjunctive treatment of congestive heart failure (CHF) and systemic or pulmonary hypertension, its primary application in modern veterinary medicine is the management of lower urinary tract disease.
Clinical Pearls:
- Urethral Relaxation: Prazosin is highly effective at relaxing the smooth muscle of the internal urethral sphincter. It is a staple in treating functional urethral obstruction, particularly in "blocked cats" (feline idiopathic cystitis/FLUTD) and dogs with reflex dyssynergia or prostatic disease.
- Cardiovascular Profile: Unlike hydralazine, prazosin dilates both the arterial and venous sides and does not typically trigger reflex tachycardia or increase renin release.
Mechanism of action
Prazosin competitively binds to and blocks post-synaptic alpha-1 adrenergic receptors.
- Genitourinary Tract: Blockade of alpha-1 receptors in the trigone of the bladder and the proximal urethra → smooth muscle relaxation → decreased urethral resistance → facilitates micturition and relieves functional obstruction.
- Cardiovascular System: Blockade of alpha-1 receptors on vascular smooth muscle → vasodilation of both arterioles and veins → decreased peripheral vascular resistance (afterload) and decreased venous return (preload) → lowered systemic blood pressure and reduced right atrial pressure.
Safety & warnings
Contraindications
- Preexisting hypotensive conditions
- Pre-existing hypotension
- Hypovolemia
- Known hypersensitivity to alpha-blockers
Adverse effects
- Hypotension (including orthostatic hypotension/syncope)
- Nausea
- Constipation
- Tachyphylaxis (drug tolerance)
- Hypotension (especially first-dose effect)
- Lethargy / Weakness
- Dizziness / Syncope
- Gastrointestinal upset (vomiting, diarrhea)
- Reflex tachycardia
Precautions
MDR1/ABCB1 Mutation Warning: Anecdotal reports suggest dogs with the ABCB1 mutation may be overly sensitive to prazosin. Consider alternate drugs or reduce dosage and increase monitoring (especially blood pressure).
- Use with caution in patients with chronic renal failure.
- Use with caution in patients with preexisting hypotensive conditions.
- First-Dose Effect: Syncope secondary to orthostatic hypotension can occur after the first dose. Monitor closely.
Drug interactions
May enhance the postural hypotensive effects seen after the first dose of prazosin
May decrease prazosin antihypertensive effects
May increase risk for hypotension
May cause synergistic hypotensive effects when used concomitantly with prazosin
Additive hypotensive effects
Increased risk of severe hypotension
Exacerbation of postural hypotension
Profound hypotension
Monitoring
- Baseline thoracic radiographs
- Mucous membrane color
- Capillary refill time (CRT)
- Arterial blood pressure
- Venous PO2 (if possible)
- Systemic blood pressure
- Heart rate
- Urine output and ease of urination (if used for urethral spasm)
Pharmacokinetics
Half-life
Absorption
Variably absorbed after oral administration in humans. Peak levels occur in 2-3 hours.
Distribution
Widely distributed throughout the body; approximately 97% bound to plasma proteins. Minimally distributed into milk. Unknown if it crosses the placenta.
Metabolism
Metabolized in the liver; some metabolites have pharmacologic activity.
Elimination
Metabolites and some unchanged drug (5-10%) are primarily eliminated in feces via the bile.
Overdose
Based on ASPCA APCC data (2008-2009):
- Dogs: Common findings include hyperactivity, tachycardia, hyperthermia, panting, and agitation.
- Cats: Common findings include tachycardia.
Treatment:
- Evacuate gastric contents and administer activated charcoal using standard precautionary measures if ingestion was recent and cardiovascular status is stable.
- Monitor heart rate and blood pressure.
- Treat shock using volume expanders and pressor agents if necessary.
- Monitor and support renal function.
Available products
Formulations
- Capsules
- 0.5 mg oral tablet
- 1 mg oral tablet
- 2 mg oral tablet
Human-labeled
- Prazosin Capsules: 1 mg, 2 mg & 5 mg (as base); Minipress® (Pfizer); generic
- Hypovase 0.5 mg, 1 mg, 2 mg, 5 mg tablets
- Prazosin 0.5 mg, 1 mg, 2 mg, 5 mg tablets
Regulatory status
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Prazosin capsules should be stored in well-closed containers at room temperature.
Client information
- Purpose: This medication is most commonly prescribed to help relax the urinary tract, making it easier for your pet to urinate (especially in cats recovering from a urinary blockage).
- Administration: Give this medication exactly as directed by your veterinarian. If possible, give the medication with food.
- First-Dose Effect: Prazosin can cause a sudden drop in blood pressure, especially after the first dose. Your pet may appear dizzy, weak, or lethargic. Keep them away from stairs or high places initially to prevent falls.
- When to call the vet: Notify your veterinarian immediately if your pet's condition deteriorates, if they are unable to urinate, or if they become excessively lethargic or depressed.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.