Prazosin

# Prazosin ## Overview - **Classification**: Alpha-1 adrenergic blocker (alpha-1 antagonist) - **Mechanism**: Selectively blocks postsynaptic alpha-1 adrenergic receptors, leading to vasodilation, decreased peripheral vascular resistance, and lowered blood pressure. ## Primary Indications 1. **Hypertension**: Management of essential hypertension. 2. **PTSD-associated Nightmares (Off-label)**: Reduction of hyperarousal and nightmares in post-traumatic stress disorder. ## Adult Dosing ### Standard Dosing **Hypertension** - **Dose**: Initial **1 mg** - **Frequency**: Once daily at bedtime - **Route**: Oral - **Titration**: Increase slowly to **1 mg** PO BID or TID, then up to **20 mg/day** in divided doses. - **Maximum**: Usually **20 mg/day** total, rarely up to 40 mg/day for severe HTN. **PTSD-associated Nightmares (Off-label)** - **Dose**: Initial **1 mg** - **Frequency**: Once daily at bedtime - **Route**: Oral - **Titration**: Increase by **1-2 mg** every 3-7 days. - **Target Dose**: **1-5 mg** PO at bedtime. Some patients may require up to **10-15 mg** at bedtime. - **Maximum**: **20 mg/day** total. ### Dose Adjustments - **Renal Impairment**: Use with caution. Start with **lowest dose (1 mg)**. No specific adjustment guidelines. - **Hepatic Impairment**: Use with caution. Start with **lowest dose (1 mg)**. Monitor closely. - **Elderly Patients**: Increased sensitivity to hypotensive effects. Start with **lowest dose (1 mg)** and titrate slowly. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Not established. - **Special Notes**: Generally avoided due to lack of data and potential for severe hypotension. ### Infants (1-12 months) - **Dose**: Not established. - **Special Notes**: Generally avoided. Use only if clearly indicated and with extreme caution. ### Children (1-12 years) - **Hypertension (Off-label)** - **Dose**: Initial **0.05-0.1 mg/kg/dose** - **Frequency**: Twice or three times daily (BID-TID) - **Maximum Single Dose**: **0.5 mg/kg** (up to **7.5 mg**) - **Maximum Daily Dose**: **0.5 mg/kg/day** (up to **20 mg/day** total) - **Special Notes**: Titrate slowly; monitor for first-dose syncope. - **PTSD (Off-label)** - **Dose**: Initial **0.5-1 mg** - **Frequency**: Once daily at bedtime - **Titration**: Increase by **0.5-1 mg** every 3-7 days. - **Maximum**: **20 mg/day** total. ### Adolescents (13-18 years) - **Dose**: Start with adult initial dose of **1 mg**. - **Frequency**: Once daily at bedtime. - **Titration**: Titrate cautiously to effect. - **Maximum**: **20 mg/day** total. - **Special Notes**: Close monitoring for orthostatic hypotension. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to prazosin or other quinazoline derivatives (e.g., terazosin, doxazosin). ### Common Adverse Effects - **Very Common (>10%)**: Dizziness, headache, drowsiness. - **Common (1-10%)**: Nausea, palpitations, fatigue, weakness, lightheadedness, dry mouth. - **Serious but Rare**: First-dose syncope (severe orthostatic hypotension), priapism. ### Key Drug Interactions - **Other Antihypertensives (e.g., diuretics, beta-blockers)**: Additive hypotensive effects. Monitor BP closely; consider dose reduction of prazosin or other agent. - **PDE5 inhibitors (e.g., sildenafil, tadalafil)**: Increased risk of symptomatic hypotension. Administer at least 4-6 hours apart. - **Alcohol**: Enhances hypotensive effect. Advise caution or avoidance. ## Monitoring & Follow-up - **Before Treatment**: Baseline orthostatic blood pressure (sitting and standing), renal and hepatic function. - **During Treatment**: Blood pressure (sitting and standing) regularly, especially after initial dose and dose increases. - **Clinical Signs**: Monitor for dizziness, lightheadedness, syncope (especially with first dose or dose escalation), persistent priapism. ## Clinical Pearls - 💡 **First-dose Syncope**: Administer the first dose at bedtime to minimize the impact of sudden blood pressure drop. - 💡 **Slow Titration**: Always start low and titrate the dose very slowly to reduce adverse effects. - 💡 **Orthostatic Hypotension**: Counsel patients to rise slowly from sitting or lying positions. Avoid rapid position changes. - 💡 **Driving/Operating Machinery**: Advise caution until patients know how prazosin affects them. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.