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# Prazosin
## Overview
Prazosin is a selective alpha-1 adrenergic antagonist that causes both arterial and venous vasodilation. By blocking alpha-1 receptors on vascular smooth muscle, it decreases peripheral vascular resistance.
## Primary Indications
* Hypertension (off-label/adjunctive).
* Benign Prostatic Hyperplasia (BPH).
* PTSD-associated nightmares and sleep disturbances.
* Raynaud’s phenomenon (off-label).
## Adult Dosing
* **Hypertension:** Initially 1 mg at bedtime to minimize "first-dose phenomenon." Gradually increase to 6–15 mg/day in divided doses. Maximum dose is typically 20 mg/day.
* **BPH:** Initial 1 mg at bedtime. Titrate gradually to 2 mg twice daily. Maximum 10 mg/day.
* **PTSD-associated nightmares:** Initial 1 mg at bedtime. Titrate every 3–7 days as tolerated. Therapeutic range is often 2–10 mg at bedtime.
## Pediatric Dosing
* **Hypertension:** 0.05–0.1 mg/kg/day divided every 6–12 hours. Start at 0.05 mg/kg/day, titrating up to a maximum of 0.5 mg/kg/day or 15 mg/day.
* **PTSD-associated nightmares:** Limited data. Often initiated at 0.5 mg or 1 mg at bedtime, titrated based on clinical response and blood pressure tolerance.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No formal standardized dosing adjustments exist, but use with caution; initiate at the lowest possible dose and titrate slowly due to increased risk of hypotension.
## Contraindications
* Known hypersensitivity to prazosin or other quinazolines (e.g., terazosin, doxazosin).
* History of syncope during initial dosing ("first-dose phenomenon").
## Adverse Effects
* **Common:** Dizziness, headache, drowsiness, weakness, palpitations, nausea.
* **Serious:** Orthostatic hypotension (severe), syncope (most common with the first dose or after rapid dose escalation), reflex tachycardia, priapism.
## Key Drug Interactions
* **Antihypertensives:** Additive hypotensive effects; monitor blood pressure closely.
* **PDE-5 Inhibitors (e.g., Sildenafil, Tadalafil):** Increased risk of symptomatic hypotension; separate dosing or exercise extreme caution.
* **Alpha-blockers:** Concomitant use with other alpha-blockers is not recommended.
## Monitoring
* **Baseline:** Blood pressure (supine and standing).
* **Ongoing:** Monitor for orthostatic symptoms, especially after dose increases.
* **Specific:** For PTSD, monitor sleep quality and latency; screen for daytime somnolence.
## Clinical Pearls
* **First-Dose Phenomenon:** Counsel patients to take the first dose while lying down or at bedtime. Symptomatic orthostasis can occur within 30–90 minutes of the first dose.
* **Titration:** Always "start low and go slow" to avoid syncope.
* **Off-label use:** Prazosin is widely utilized in psychiatry for nightmares; efficacy for core PTSD symptoms (re-experiencing, hyperarousal) is debated, but sleep benefit is well-documented.
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**Disclaimer:** This information is for educational purposes only. Drug dosing, local protocols, and clinical guidelines change frequently. Always verify specific dosing and patient-specific safety considerations using current, official prescribing information (e.g., FDA labels) or institutional pharmacy resources before administration.
