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# Prazosin
## Overview
Prazosin is a selective alpha-1 adrenergic antagonist that causes both arterial and venous vasodilation. It is frequently used for hypertension and, increasingly, off-label for PTSD-associated nightmares.
## Primary Indications
* **FDA Approved:** Hypertension.
* **Off-label:** PTSD-associated nightmares/sleep disturbances, BPH (less commonly used than tamsulosin/terazosin), Raynaud phenomenon.
## Adult Dosing
* **Hypertension:** Start 1 mg at bedtime to minimize first-dose syncope. Titrate slowly based on response. Usual maintenance: 6–15 mg/day in divided doses. Maximum dose: 20 mg/day.
* **PTSD-associated Nightmares:** Start 1 mg at bedtime. Titrate every few days as tolerated. Often effective in the 2–10 mg range.
## Pediatric Dosing
* **Hypertension (Off-label):** Initial: 0.05 mg/kg/day divided into 2–4 doses. Titrate slowly to a maximum of 0.5 mg/kg/day or 15–20 mg/day.
* *Note:* Pediatric dosing is highly variable and depends on institutional protocols; consult a pediatric specialist.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No specific standard formula; initiate at the lowest possible dose (1 mg) and titrate with extreme caution due to increased risk of orthostatic hypotension.
## Contraindications
* Hypersensitivity to prazosin or other quinazolines (e.g., terazosin, doxazosin).
## Adverse Effects
* **Common:** Dizziness, headache, drowsiness, lassitude, palpitations, nausea.
* **Serious:** First-dose phenomenon (pronounced orthostatic hypotension, syncope, tachycardia within 30–90 minutes of initial dose), priapism, fluid retention.
## Key Drug Interactions
* **PDE-5 Inhibitors (e.g., sildenafil, tadalafil):** Increases risk of symptomatic hypotension.
* **Antihypertensives:** Synergistic hypotensive effect; requires close monitoring.
* **Beta-blockers:** May increase the incidence of first-dose syncope.
## Monitoring
* **Blood Pressure:** Monitor standing and seated BP, especially during initiation or dose titration to assess for orthostasis.
* **Symptoms:** Monitor for dizziness, sleep quality improvements (in PTSD), and sexual side effects.
## Clinical Pearls
* **First-Dose Phenomenon:** Always instruct patients to take the first dose (or any dose increase) at bedtime to sleep through potential syncope/tachycardia.
* **Titration:** "Start low, go slow" is the golden rule for alpha-blockers.
* **Absorption:** Bioavailability can be influenced by food; consistency in administration (with or without food) is recommended.
* **Off-label Use:** For PTSD, efficacy is generally observed in reducing frequency and intensity of trauma-related nightmares rather than PTSD core symptoms (re-experiencing/avoidance).
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**Disclaimer:** This information is for educational purposes and does not replace professional clinical judgment. Always verify dosages and contraindications against current institutional guidelines and the manufacturer’s full prescribing information (PI) before ordering or administering medication.
