What is the maximum dose of prazosin?

Maximum Dose of Prazosin

The maximum dose of prazosin is 20 mg per day, typically divided into 2-3 doses for hypertension, though higher single bedtime doses up to 20 mg have been used in PTSD-related nightmare protocols. 1

FDA-Approved Maximum Dosing

• The FDA label establishes 20 mg per day as the usual maximum recommended human dose for prazosin 1
• For hypertension management, this is administered in 2-3 divided doses throughout the day 2, 1
• The American College of Cardiology confirms the 2-20 mg per day range in 2-3 divided doses when treating hypertension with concomitant benign prostatic hyperplasia 2

Context-Specific Maximum Dosing

For Hypertension

• Clinical studies demonstrate optimal effectiveness at 3-8 mg/day rather than higher doses of 9-20 mg/day, suggesting that exceeding moderate doses may not provide additional benefit 3
• Individual studies have used doses ranging from 3-20 mg daily for hypertension, with 8-10 mg/day considered an optimum regimen 4
• Doses as high as 9 mg/day have been used for benign prostatic hyperplasia 5

For PTSD-Related Nightmares

• The American Academy of Sleep Medicine reports that in large VA studies, prazosin was escalated to a maximum of 20 mg as a single bedtime dose 6
• Mean achieved doses in military veterans ranged from 14.8-15.6 mg for men and 7.0 mg for women, all below the 20 mg maximum 6, 7
• Civilians with PTSD typically require much lower doses (mean 3.1 mg), while military veterans often need 9.5-15.6 mg/day 7, 8

Critical Dosing Considerations

First-Dose Phenomenon

• Always start at 1 mg at bedtime to minimize risk of first-dose syncope, which occurred in 0.15% (1 in 667) of patients in clinical experience with 22,000 patients 9
• The FDA label emphasizes reducing prazosin to 1-2 mg three times daily when adding other antihypertensive agents, then retitrating based on response 1

Special Populations

• Elderly patients require lower doses and careful blood pressure monitoring due to increased susceptibility to orthostatic hypotension 2, 8
• Patients with impaired renal function do not require dose adjustment, as prazosin elimination is not impaired in renal failure 3
• Concomitant use with phosphodiesterase-5 inhibitors can cause additive hypotension and requires caution 1

Monitoring at Maximum Doses

• Monitor blood pressure after initial dose and with each significant dose increase 7, 8
• Be alert for dizziness, lightheadedness, and orthostatic hypotension, especially at higher doses 7, 8
• For PTSD treatment, assess nightmare frequency using standardized measures when possible 7

Important Caveats

• The 20 mg maximum applies regardless of indication (hypertension, BPH, or PTSD nightmares) 1
• Doses above 8-10 mg/day for hypertension may not provide additional benefit and could increase side effects 4, 3
• Fluid retention may develop on long-term therapy and necessitate adding a diuretic 9
• Sexual dysfunction is uncommon with prazosin compared to other antihypertensives 9