Prazosin

Alpha-1 Antagonist·Cardiovascular - Vasodilators

Resistant hypertension, Raynaud's

PBSALPHA-1Minipress1 mg tabletS4+1

Max Dose

20 mg/day

Half-life

2–3 h

First-Dose Drop

HIGH

PTSD

OFF-LABEL

Rapid Summary

Overview

Highly potent, short-acting alpha-1 receptor antagonist. Causes massive vasodilation. Notorious for severe first-dose syncope.

Maximum Dose

Max 20 mg/day (given in divided doses).

Clinical Focus

The first dose MUST be given at NOCTE while the patient is lying in bed to prevent collapse.

Bottom Line

Prazosin is useful as an adjunct antihypertensive and for PTSD-related nightmares, but severe first-dose hypotension mandates starting at bedtime with a low dose.

Formulation & Access

Brand Names

Minipress

Oral Routes

Tablets (1 mg, 2 mg, 5 mg).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Resistant hypertension, Raynaud's.

Off-Label

OFF

PTSD-associated nightmares, BPH.

Clinical Place

Rarely used for BP monotherapy due to tachyphylaxis. Now heavily utilised in psychiatry for trauma nightmares.

Quick reference

Class & Role

Alpha-1 Antagonist — Highly potent, short-acting alpha-1 receptor antagonist.

Route / Formulation

Tablets (1 mg, 2 mg, 5 mg). (Minipress)

Usual Dose & Max

Start PO 0.5 mg NOCTE for 3-7 days. Maintenance 0.5-1 mg BD or TDS. Max 20 mg/day.

Key Indication Doses

Hypertension: Start PO 0.5 mg NOCTE for 3-7 days. Maintenance 0.5-1 mg BD or TDS. Max 20 mg/day. PTSD / Nightmares (Off-Label): Start PO 0.5 mg NOCTE. Titrate up to 1-5 mg NOCTE. BPH: PO 0.5 mg BD (though tamsulosin is superior).

Best Uses

Prazosin is useful as an adjunct antihypertensive and for PTSD-related nightmares, but severe first-dose hypotension mandates starting at bedtime with a low dose.

Avoid / Cautions

History of micturition syncope. Pregnancy Category B2.

Key Risks

Cardiovascular: First-dose severe orthostatic hypotension (syncope). MODERATE — Palpitations, peripheral oedema. Neurological: Dizziness, drowsiness. Genitourinary: Priapism, retrograde ejaculation.

Key Interactions

PDE-5 Inhibitors (Sildenafil/Viagra) cause severe, refractory hypotension if given within 4 hours of Prazosin. Additive effects with beta-blockers and diuretics.

Monitoring

Postural BP checks. Ensure the patient is educated to get up slowly from sitting/lying. No specific routine laboratory tests required.

Clinical Pearl

The first dose causes a profound loss of venomotor tone. If the patient stands up, blood pools in the legs, and they will faint. Must be taken strictly in bed.

Access

Minipress1 mg tablet

Brand: Minipress
Formulation: Tablets (1 mg, 2 mg, 5 mg)

Prazosin

Alpha-1 Antagonist·Cardiovascular - Vasodilators

Resistant hypertension, Raynaud's

PBSALPHA-1Minipress1 mg tabletS4+1

Max Dose

20 mg/day

Half-life

2–3 h

First-Dose Drop

HIGH

PTSD

OFF-LABEL

Rapid Summary

Overview

Highly potent, short-acting alpha-1 receptor antagonist. Causes massive vasodilation. Notorious for severe first-dose syncope.

Maximum Dose

Max 20 mg/day (given in divided doses).

Clinical Focus

The first dose MUST be given at NOCTE while the patient is lying in bed to prevent collapse.

Bottom Line

Prazosin is useful as an adjunct antihypertensive and for PTSD-related nightmares, but severe first-dose hypotension mandates starting at bedtime with a low dose.

Formulation & Access

Brand Names

Minipress

Oral Routes

Tablets (1 mg, 2 mg, 5 mg).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Resistant hypertension, Raynaud's.

Off-Label

OFF

PTSD-associated nightmares, BPH.

Clinical Place

Rarely used for BP monotherapy due to tachyphylaxis. Now heavily utilised in psychiatry for trauma nightmares.

Quick reference

Class & Role

Alpha-1 Antagonist — Highly potent, short-acting alpha-1 receptor antagonist.

Route / Formulation

Tablets (1 mg, 2 mg, 5 mg). (Minipress)

Usual Dose & Max

Start PO 0.5 mg NOCTE for 3-7 days. Maintenance 0.5-1 mg BD or TDS. Max 20 mg/day.

Key Indication Doses

Best Uses

Prazosin is useful as an adjunct antihypertensive and for PTSD-related nightmares, but severe first-dose hypotension mandates starting at bedtime with a low dose.

Avoid / Cautions

History of micturition syncope. Pregnancy Category B2.

Key Risks

Key Interactions

PDE-5 Inhibitors (Sildenafil/Viagra) cause severe, refractory hypotension if given within 4 hours of Prazosin. Additive effects with beta-blockers and diuretics.

Monitoring

Postural BP checks. Ensure the patient is educated to get up slowly from sitting/lying. No specific routine laboratory tests required.

Clinical Pearl

The first dose causes a profound loss of venomotor tone. If the patient stands up, blood pools in the legs, and they will faint. Must be taken strictly in bed.

Access

Minipress1 mg tablet

Brand: Minipress
Formulation: Tablets (1 mg, 2 mg, 5 mg)