What is the recommended dosing for Prazosin (alpha-blocker) in treating hypertension and benign prostatic hyperplasia?

Prazosin Dosing

Prazosin is NOT recommended for benign prostatic hyperplasia due to insufficient evidence, but IS recommended for PTSD-associated nightmares and can be used for hypertension at 2-20 mg daily in divided doses.

For Hypertension

The FDA-approved dosing regimen for hypertension requires careful titration to avoid first-dose hypotension 1:

Initial Dosing

• Start with 1 mg two or three times daily to minimize orthostatic hypotension risk 1
• The first dose should be given at bedtime to reduce first-dose syncope 2

Maintenance Dosing

• Therapeutic range: 6-15 mg daily in divided doses (most commonly used) 1
• Maximum: 20 mg daily in divided doses, though some patients may benefit from up to 40 mg daily 1
• Requires 2-3 times daily administration for adequate 24-hour blood pressure control 2

Titration Strategy

• Increase slowly after initial dosing period 1
• When adding other antihypertensives, reduce prazosin to 1-2 mg three times daily and retitrate 1

For Benign Prostatic Hyperplasia

The AUA guidelines explicitly state that data are insufficient to support prazosin use for BPH 3. Instead, use alfuzosin, doxazosin, tamsulosin, or terazosin, which have established efficacy 3.

Why Prazosin Is Not Recommended for BPH

• Lack of rigorous clinical trial data compared to other alpha-blockers 3
• Other alpha-1 blockers (doxazosin, terazosin, tamsulosin, alfuzosin) have been extensively studied and produce 4-6 point improvements in AUA Symptom Index 3

For PTSD-Associated Nightmares

Prazosin is recommended (Level A evidence) for PTSD-related nightmares 3:

Dosing Protocol

• Start with 1 mg at bedtime 3
• Increase by 1-2 mg every few days until effective 3
• Average effective dose: approximately 3 mg (range 1 mg to over 10 mg) 3
• Higher doses used in some trials: mean 9.5-13.3 mg/day for severe PTSD 3
• Some protocols include mid-morning dosing in addition to bedtime administration 2

Critical Safety Considerations

Orthostatic Hypotension Monitoring

• Both elderly patients and those on multiple medications are at highest risk 4
• Monitor blood pressure closely, especially after initiation or dose changes 4
• Watch for dizziness and lightheadedness when standing 4

Drug Interactions

• Combining with PDE-5 inhibitors requires starting the PDE-5 inhibitor at lowest dose due to additive hypotensive effects 1
• Combining with other CNS depressants (like doxepin) may cause additive sedation and orthostatic hypotension 4

Common Pitfalls to Avoid

• Never start with doses higher than 1 mg to prevent first-dose syncope 1
• Avoid abrupt discontinuation, though prazosin does not cause withdrawal phenomena like clonidine 2
• Do not assume prazosin adequately treats hypertension in patients with cardiac risk factors—separate management may be needed 3
• Be especially cautious in elderly patients who are more susceptible to falls from orthostatic hypotension 4, 2