What is the recommended dosage and usage of Prazosin for patients with hypertension, benign prostatic hyperplasia, or post-traumatic stress disorder (PTSD)-related nightmares, considering potential side effects and interactions?

Prazosin: Dosing and Usage Recommendations

Indication-Specific Dosing

PTSD-Associated Nightmares (Primary Indication)

Prazosin is recommended as first-line pharmacologic treatment for PTSD-associated nightmares, starting at 1 mg at bedtime and titrating by 1-2 mg every few days until clinical response is achieved. 1, 2

Dosing algorithm:

• Start: 1 mg at bedtime to minimize first-dose hypotension 1, 2
• Titration: Increase by 1-2 mg every few days based on nightmare frequency and blood pressure tolerance 1, 2
• Target doses vary by population:
  • Civilian trauma victims: 3-4 mg/day (mean 3.1 ± 1.3 mg) 2, 3
  • Military veterans: 9.5-15.6 mg/day 1, 2
  • Active-duty men: 15.6 ± 6.0 mg 2
  • Active-duty women: 7.0 ± 3.5 mg 2
• Maximum studied dose: Over 10 mg/day in some trials, with mean doses up to 13.3 mg/day in veterans 1

Monitoring requirements:

• Check blood pressure after initial dose and with each significant increase 2, 3
• Assess nightmare frequency using standardized measures (e.g., CAPS Item #2) 1
• Monitor for orthostatic hypotension, especially in elderly or those on concurrent antihypertensives 1, 2

Hypertension

For hypertension, prazosin should be dosed 2-3 times daily starting at 1 mg per dose, with maintenance doses typically 6-15 mg/day in divided doses. 4

Dosing algorithm per FDA labeling:

• Initial: 1 mg two or three times daily 4
• Maintenance: 6-15 mg/day in divided doses (most common therapeutic range) 4
• Maximum: 20 mg/day typically; rarely up to 40 mg/day in divided doses 4
• With other antihypertensives: Reduce to 1-2 mg three times daily and retitrate 4

Critical caveat: In men with hypertension and cardiac risk factors, doxazosin (a related alpha-blocker) was associated with higher incidence of congestive heart failure compared to other antihypertensives, so alpha-blocker monotherapy should not be assumed to constitute optimal hypertension management 1

Benign Prostatic Hyperplasia (BPH)

Prazosin is NOT recommended for BPH treatment—insufficient data support its use compared to other alpha-blockers. 1

The 2003 AUA guideline explicitly states that "data are insufficient to support a recommendation for the use of prazosin" for LUTS secondary to BPH 1. Instead, alfuzosin, doxazosin, tamsulosin, and terazosin are appropriate options with equal clinical effectiveness 1. While older research from 1990 showed 60-70% of patients benefited from prazosin 1-9 mg/day for BPH 5, this has been superseded by guideline recommendations favoring other alpha-blockers with better evidence 1.

Critical Drug Interactions and Contraindications

Key interactions to avoid or manage:

• PDE-5 inhibitors (sildenafil, tadalafil, etc.): Can cause additive hypotension; start PDE-5 inhibitor at lowest dose if patient is on prazosin 4
• SSRIs: May diminish prazosin's response in PTSD patients 2, 3
• Other antihypertensives: Require dose reduction of prazosin to 1-2 mg three times daily with retitration 4

Common Side Effects and Management

Most frequent adverse effects:

• Orthostatic hypotension and dizziness: Most common, especially after first dose or dose increases 1, 2, 6
  • Management: Take first dose at bedtime, limit initial dose to 1 mg, withhold diuretics for 1 day before starting 6
  • Syncope occurs in only 0.15% (1 in 667 patients) when 1 mg initial dose is used 6
• Ejaculatory dysfunction: Less common than with other alpha-blockers 1
• Nasal congestion, tiredness (asthenia): Mild and transient 1, 6

Important clinical note: Nightmares return to baseline if prazosin is discontinued—this is not a curative treatment 2, 3

Special Populations

Elderly or those on concurrent antihypertensives:

• Use lower initial doses 2
• Monitor blood pressure more frequently 2, 3

Renal impairment:

• Prazosin is effective and safe in hypertensive patients with renal dysfunction 7
• No deterioration in renal function attributable to prazosin was observed in studies 7

What Prazosin Is NOT For

Do not use prazosin as a general anxiolytic—it is not indicated and will not work for non-trauma anxiety. 3 Prazosin treats nightmare disorder with secondary benefits on PTSD symptoms, not anxiety directly 3. For general anxiety, SSRIs/SNRIs are first-line per American Psychiatric Association guidelines 3.