Please check your internet connection and try again.
# Prazosin
## Overview
Prazosin is a selective, competitive antagonist of postsynaptic alpha-1 adrenergic receptors. It causes peripheral vasodilation (both arterial and venous), reducing systemic vascular resistance and blood pressure. It is also used off-label for its central effects in managing PTSD-associated nightmares.
## Primary Indications
* **Hypertension** (Not a first-line agent).
* **Benign Prostatic Hyperplasia (BPH)** (Off-label/Less common due to newer agents).
* **PTSD-associated insomnia and nightmares** (Off-label).
## Adult Dosing
* **Hypertension:** Initially 1 mg at bedtime to minimize "first-dose phenomenon." Titrate slowly up to a typical maintenance range of 6–15 mg/day in divided doses. Maximum: 20 mg/day.
* **PTSD-associated Nightmares:** Initially 1 mg at bedtime. Titrate every 3–7 days as tolerated. Maintenance dose is typically 2–10 mg at bedtime. Maximum: 20 mg/day (varies by clinical practice/protocol).
## Pediatric Dosing
* **Hypertension (Off-label):** Initial: 0.05–0.1 mg/kg/day divided every 6–8 hours. Titrate as needed. Max: 0.5 mg/kg/day or 15 mg/day.
* **PTSD-associated Nightmares (Off-label):** Limited evidence. Dosing often starts at 0.5–1 mg at bedtime, titrated based on clinical response and tolerability.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustments established, but start with lower doses and titrate cautiously due to increased sensitivity to hypotensive effects.
* **Hepatic Impairment:** Use caution; systemic clearance may be reduced.
## Contraindications
* Known hypersensitivity to prazosin or other quinazolines (e.g., terazosin, doxazosin).
## Adverse Effects
* **"First-Dose Phenomenon":** Severe orthostatic hypotension and syncope occurring 30–90 minutes after the initial dose or following a dose increase.
* **Common:** Dizziness, headache, drowsiness, palpitations, nausea, and peripheral edema.
* **Rare/Serious:** Priapism (prolonged, painful erections).
## Key Drug Interactions
* **PDE-5 Inhibitors (e.g., Sildenafil, Tadalafil):** Significant risk of severe hypotension when combined.
* **Antihypertensives:** Additive hypotensive effects with diuretics, beta-blockers, and calcium channel blockers.
* **CYP3A4 Inhibitors:** May increase prazosin concentrations (use caution).
## Monitoring
* **Blood Pressure:** Assess in both sitting and standing positions, especially during dose initiation and titration.
* **Symptoms:** Monitor for syncope, dizziness, and nocturnal symptoms (nightmares) in PTSD patients.
## Clinical Pearls
* **First-Dose Precautions:** Always administer the first dose at bedtime to minimize the impact of orthostatic syncope. Ensure patients are aware of the risk of falls.
* **Drug Half-Life:** Prazosin has a relatively short half-life (~2–3 hours), necessitating multiple daily doses for hypertension, whereas it is dosed once daily for nightmares.
* **Efficacy:** In PTSD, the drug is specifically targeted at reducing sleep disturbances related to hyperarousal and nightmares; it does not replace core PTSD psychotherapies.
***
**Disclaimer:** This information is for educational purposes and does not replace professional clinical judgment. Dosing protocols may vary by institution. Always consult the most current version of the FDA-approved package insert or a clinical drug database (e.g., Lexicomp, Micromedex) before prescribing or administering medication.
