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# Prazosin
## Overview
Prazosin is a selective alpha-1 adrenergic receptor antagonist.
## Primary Indications
* Hypertension
* Symptomatic benign prostatic hyperplasia (BPH)
* Off-label: PTSD-related nightmares
## Adult Dosing
* **Hypertension:** Start with 1 mg orally once or twice daily. Titrate gradually based on blood pressure response. Usual maintenance dose is 1-5 mg twice daily. Maximum dose is typically 10 mg twice daily, though higher doses may be used cautiously under specialist supervision.
* **BPH:** Start with 1 mg orally once or twice daily. Titrate gradually. Usual maintenance dose is 1-5 mg twice daily. Maximum dose is typically 10 mg twice daily.
* **PTSD Nightmares:** Start with 1 mg orally at bedtime. Titrate upwards as needed and tolerated, often to 4-10 mg at bedtime. Doses can range from 1 mg to 16 mg per night.
## Pediatric Dosing
Dosing in children is not well-established and should be managed by a pediatric specialist. Limited data suggests potential use for hypertension in children, but no standard dosing exists.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is usually recommended, but caution and closer monitoring are advised, particularly in severe impairment.
* **Hepatic Impairment:** Use with caution; no specific adjustments are typically provided.
## Contraindications
* Known hypersensitivity to prazosin or other quinazoline derivatives.
## Adverse Effects
* **Common:** Dizziness, lightheadedness (especially orthostatic hypotension), headache, drowsiness, weakness, palpitations, nausea.
* **Serious:** Syncope (especially with first dose or dose escalation), severe orthostatic hypotension, priapism (rare).
## Key Drug Interactions
* **Other Antihypertensives:** Additive hypotensive effects.
* **Beta-blockers:** May increase the risk of severe orthostatic hypotension with the first dose of prazosin.
* **Diuretics:** Additive hypotensive effects.
* **PDE5 Inhibitors (e.g., sildenafil):** Increased risk of symptomatic hypotension and syncope. Avoid concurrent use or use with extreme caution and a reduced prazosin dose.
## Monitoring
* Blood pressure (lying and standing) before and after dose initiation/titration.
* Symptoms of dizziness or syncope.
* Renal function if clinically indicated.
## Clinical Pearls
* The "first-dose phenomenon" (marked hypotension and syncope) can occur shortly after the initial dose or with subsequent dose increases. Advise patients to take the first dose at bedtime and to avoid driving or operating machinery for 24 hours after the first dose or any dose increase.
* Gradual titration is essential to minimize orthostatic hypotension.
* Dosing frequency may be twice daily for hypertension and BPH, but once daily at bedtime is common for PTSD nightmares.
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*Please verify current prescribing information for definitive guidance.*
