What is the starting dose of Prazosin for adults with hypertension or benign prostatic hyperplasia?

Prazosin Starting Dose for Hypertension and BPH

The recommended starting dose of prazosin for adults with hypertension or benign prostatic hyperplasia is 1 mg two or three times a day. 1

Dosing Considerations for Hypertension

Prazosin is classified as an alpha-1 blocker and is considered a secondary agent for hypertension management according to the 2017 ACC/AHA guidelines. The dosing protocol follows a specific pattern:

• Initial dose: 1 mg two or three times daily 2, 1
• Maintenance dose: Can be slowly increased to a total daily dose of 20 mg given in divided doses 1
• Usual effective range: 6-15 mg daily in divided doses 1
• Maximum dose: 20 mg daily (doses higher than this rarely increase efficacy) 1
• Administration frequency: 2-3 times daily 2

Important Safety Considerations

The low starting dose is critical as prazosin can cause syncope with sudden loss of consciousness, particularly within 30-90 minutes of the initial dose. This "first-dose phenomenon" occurs in approximately 1% of patients given an initial dose of 2 mg or greater 1. To minimize this risk:

• Always start with 1 mg capsules 1
• Increase dosage slowly 1
• Introduce additional antihypertensive drugs with caution 1
• Monitor for orthostatic hypotension, especially in older adults 2

Dosing for Benign Prostatic Hyperplasia (BPH)

For BPH treatment, prazosin may be considered as a second-line agent:

• Initial dose: Same as for hypertension - 1 mg two or three times daily 1
• Effective dose range: 1-5 mg daily in divided doses 3, 4
• Clinical efficacy: Studies show 60-70% of patients experience symptom improvement 3

Alpha-1 blockers like prazosin work by blocking alpha-1 receptors in the prostate tissue, reducing smooth muscle contractions that contribute to urinary obstruction 3. Clinical studies have demonstrated improvements in:

• Urinary flow rates
• Decreased urethral pressure
• Reduced obstructive and irritative symptoms 3, 5, 6

Monitoring and Titration

When initiating prazosin therapy:

1. Begin with 1 mg doses
2. Monitor blood pressure and symptoms for 2-4 hours after the first dose
3. Increase dose gradually every few days as needed
4. If adding other antihypertensive agents, reduce prazosin dose to 1-2 mg three times daily and retitrate 1

Special Considerations

• Prazosin is associated with orthostatic hypotension, particularly in older adults 2
• It may cause dizziness and lightheadedness, especially during initial therapy 1
• Caution patients about these potential side effects and advise them to avoid situations where injury could result from syncope 1
• Prazosin should not be used in combination with PDE-5 inhibitors without dose adjustment due to risk of additive hypotensive effects 1

Alternative Options

For hypertension management, the ACC/AHA guidelines recommend ACE inhibitors, ARBs, calcium channel blockers, or thiazide diuretics as preferred first-line agents over alpha-1 blockers 7.

For BPH, tamsulosin (0.4 mg daily) is often preferred over prazosin due to its once-daily dosing and minimal effects on blood pressure 7, 4.