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# Prazosin
## Overview
Prazosin is a selective, competitive alpha-1 adrenergic antagonist. By blocking postsynaptic alpha-1 receptors, it causes both arterial and venous vasodilation, resulting in decreased peripheral vascular resistance and blood pressure.
## Primary Indications
* **Hypertension:** (Off-label for management of resistant cases).
* **Benign Prostatic Hyperplasia (BPH):** Symptomatic relief (not first-line).
* **Post-Traumatic Stress Disorder (PTSD):** Management of trauma-related nightmares and sleep disturbances.
## Adult Dosing
* **Hypertension:** Start 1 mg at bedtime to minimize orthostatic hypotension. May increase to 6–15 mg/day in divided doses. Maximum dose is typically 20 mg/day.
* **PTSD-associated nightmares:** Start 1 mg at bedtime. Titrate every 3–7 days based on tolerance. Clinical trials often see efficacy between 5 mg and 20 mg at bedtime.
* **BPH:** Initial dose 1 mg twice daily. Maximum 10 mg/day.
## Pediatric Dosing
* **Hypertension:** Limited data. Initial dose 0.05–0.1 mg/kg/day divided every 6–8 hours. Titrate as needed; maximum 0.5 mg/kg/day or 20 mg/day. Use with extreme caution.
## Dose Adjustments
* **Renal Impairment:** No specific adjustment required, but start at the lowest possible dose due to heightened sensitivity to hypotensive effects.
* **Hepatic Impairment:** Use caution; systemic clearance may be reduced.
## Contraindications
* **Hypersensitivity:** Known allergy to prazosin or other quinazolines.
## Adverse Effects
* **First-Dose Phenomenon:** Profound orthostatic hypotension and syncope occurring 30–90 minutes after the initial dose or a dose increase.
* **Common:** Dizziness, headache, drowsiness, lack of energy, palpitations, and nausea.
* **Serious:** Priapism (rare but significant).
## Key Drug Interactions
* **Antihypertensives/Diuretics:** Potentiate hypotensive effects; risk of severe orthostasis.
* **PDE-5 Inhibitors (e.g., Sildenafil, Tadalafil):** Significant risk of severe hypotension; avoid concurrent use or ensure alpha-blocker is stable at a low dose before initiation.
* **CYP3A4 Inhibitors:** May increase prazosin serum concentrations.
## Monitoring
* **Blood Pressure:** Monitor standing and supine BP, especially during initiation and titration (anticipate orthostatic monitoring).
* **Symptomatic:** Screen for nightmares/sleep quality in PTSD patients; assess for urinary symptoms in BPH.
* **Safety:** Counsel patients to rise slowly from sitting or lying positions.
## Clinical Pearls
* **First-Dose Precautions:** Always administer the very first dose at bedtime in a controlled setting to mitigate the "first-dose effect."
* **Tolerance:** The antihypertensive effect of prazosin may diminish over time ("tachyphylaxis") as the body compensates.
* **PTSD Dosing:** Dosing for PTSD is generally titrated to clinical effect rather than blood pressure targets; however, monitor for symptomatic hypotension.
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*Disclaimer: This information is for educational purposes and does not substitute for clinical judgment. Dosing may vary by local practice protocols, age, and comorbidities. Always verify current prescribing information through official resources (e.g., FDA-approved labels or clinical decision support tools) before prescribing or administering medication.*
