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# Prazosin
## Overview
Prazosin is a selective, competitive alpha-1 adrenergic receptor antagonist. By blocking postsynaptic alpha-adrenoceptors, it causes both arterial and venous vasodilation, resulting in decreased peripheral vascular resistance.
## Primary Indications
* **Hypertension** (Off-label/secondary)
* **Benign Prostatic Hyperplasia (BPH)**
* **PTSD-associated nightmares/sleep disturbances** (Off-label)
* **Raynaud phenomenon** (Off-label)
## Adult Dosing
* **Hypertension:** Start 1 mg at bedtime to minimize "first-dose" syncope. Titrate slowly based on response. Maintenance: 6 mg to 15 mg daily in 2–3 divided doses. Maximum: 20 mg/day.
* **BPH:** Initial: 1 mg twice daily. Maintenance: 2 mg twice daily. Maximum: 10 mg/day in divided doses.
* **PTSD-associated Nightmares:** Start 1 mg at bedtime. Titrate every 3–7 days. Typical effective range: 2 mg to 10 mg at bedtime.
## Pediatric Dosing
* **Hypertension (Off-label):** Initial: 0.05 mg/kg/dose every 6–8 hours. Titrate up to 0.5 mg/kg/dose. Maximum: 10 mg/dose or 15–20 mg/day total depending on protocol.
* **PTSD/Nightmares (Off-label):** Very limited data. Some literature suggests starting at 0.5 mg to 1 mg at bedtime, increasing to 2–3 mg daily. Use caution; efficacy and safety in children are not well-established.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No formal standardized adjustments; start at the lowest possible dose (1 mg) and titrate slowly due to potential for cumulative effects and hypotension.
## Contraindications
* Hypersensitivity to prazosin or other quinazolines.
## Adverse Effects
* **First-dose phenomenon:** Orthostatic hypotension, dizziness, and syncope (typically within 30–90 minutes of the first dose).
* Common: Drowsiness, headache, palpitations, nausea, and nasal congestion.
* Rare: Priapism (requires immediate medical attention).
## Key Drug Interactions
* **PDE-5 Inhibitors (e.g., Sildenafil, Tadalafil):** Increased risk of symptomatic hypotension.
* **Antihypertensives/Diuretics:** Additive blood pressure-lowering effects (use with caution).
* **Beta-blockers:** May increase the risk of the first-dose syncope phenomenon.
## Monitoring
* Monitor blood pressure (sitting and standing) 2–4 hours after the initial dose and after dose escalations.
* Monitor symptoms of BPH or PTSD severity as indicated.
* Assess for orthostatic symptoms during routine follow-ups.
## Clinical Pearls
* **First-Dose Syncopy:** To minimize risk, advise the patient to take the first dose immediately before bed and to change positions slowly if they must rise at night.
* **Tolerance:** The therapeutic effect may diminish over time; dose adjustments may be necessary.
* **Off-label Use:** Prazosin's role in PTSD is strictly for the treatment of sleep-related symptoms (nightmares) and is not a monotherapy for PTSD.
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**Disclaimer:** This information is for educational purposes only. Always verify dosages, contraindications, and drug interactions against institutional protocols and current prescribing information (e.g., package inserts or clinical resources like UpToDate/Lexicomp) before clinical application.
