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# Prazosin
## Overview
Prazosin is a selective, competitive antagonist of alpha-1 adrenergic receptors. By blocking these receptors in vascular smooth muscle, it induces arterial and venous vasodilation, reducing systemic vascular resistance and blood pressure.
## Primary Indications
* Hypertension (off-label use as primary monotherapy, often adjunctive).
* Benign Prostatic Hyperplasia (BPH) - *Note: Alpha-1 selective blockers like tamsulosin are typically preferred.*
* PTSD-associated nightmares and sleep disturbances (off-label).
## Adult Dosing
* **Hypertension:** Start with 1 mg at bedtime to minimize "first-dose" syncope. Titrate slowly based on response (increase every 2–3 days). Usual maintenance: 6 mg to 15 mg daily in divided doses. Maximum: 20 mg/day.
* **PTSD-associated nightmares:** Start 1 mg at bedtime. Titrate by 1–2 mg every 3–7 days. Typical therapeutic range: 2 mg to 10 mg at bedtime.
## Pediatric Dosing
* **Hypertension (Off-label):** Initial dose 0.05 mg/kg/day divided every 6 hours. Titrate up to 0.5 mg/kg/day as tolerated.
* *Note: Pediatric dosing is highly variable; consult institutional protocols or specialist guidelines.*
## Dose Adjustments
* **Renal/Hepatic:** No specific standard adjustment provided by the manufacturer, but clinical caution is advised. Start at the lowest dose and titrate cautiously due to potential for significant hypotension.
## Contraindications
* Known hypersensitivity to prazosin or other quinazolines (e.g., terazosin, doxazosin).
## Adverse Effects
* **First-Dose Phenomenon:** Severe orthostatic hypotension resulting in syncope within 30–90 minutes of the first dose.
* Common: Dizziness, drowsiness, headache, palpitations, nausea, and peripheral edema.
* Rare/Serious: Priapism and tachycardia.
## Key Drug Interactions
* **PDE-5 Inhibitors:** Concomitant use with sildenafil, tadalafil, or vardenafil increases the risk of additive symptomatic hypotension; ensure patient is on a stable dose of the alpha-blocker before initiating a PDE-5 inhibitor.
* **Antihypertensives:** Potential for additive hypotensive effects with diuretics, beta-blockers, and calcium channel blockers.
## Monitoring
* **Blood Pressure:** Monitor standing and supine BP, especially during initial dose titration to detect orthostasis.
* **Symptoms:** Monitor for dizziness, lightheadedness, and syncope.
## Clinical Pearls
* **First-Dose Strategy:** Always initiate at bedtime to reduce the risk of clinical injury from orthostatic syncope. Ensure the patient understands the need to rise slowly from a sitting or lying position.
* **Tachyphylaxis:** Tolerance to the blood pressure-lowering effect may develop over time.
* **Non-hypertensive use:** When used for PTSD, patients may not require blood pressure monitoring, but postural hypotension remains a risk.
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*Disclaimer: This information is for educational purposes only. Always consult current institutional guidelines and the full prescribing information (package insert) before prescribing, administering, or making clinical decisions.*
