What is the recommended dosing for prazosin (alpha-blocker)?

Prazosin Dosing Recommendations

The recommended dosing for prazosin should start at 1 mg two or three times daily, with gradual titration to a maintenance dose of 6-15 mg daily in divided doses, not exceeding 20 mg daily for most patients. 1

General Dosing Guidelines

Initial Dosing

• Start with 1 mg two or three times daily 1
• Take first dose at bedtime to minimize first-dose hypotension risk 2
• For patients at higher risk of hypotension (elderly, recent stroke patients), consider starting at 0.5 mg 3

Titration

• Increase dose gradually based on blood pressure response
• Typical titration: increase by 1-2 mg every few days until desired effect 4

Maintenance Dosing

• Therapeutic range: 6-15 mg daily in divided doses 1
• Maximum recommended dose: 20 mg daily (higher doses rarely provide additional efficacy) 1
• After initial titration, some patients can be maintained on twice-daily dosing 1

Special Populations and Indications

PTSD-Associated Nightmares

• Initial dose: 1 mg at bedtime 4
• Increase by 1-2 mg every few days until effective 4
• Average maintenance dose for civilians: approximately 3 mg (range 1-10 mg) 4
• Military veterans may require higher doses: 9.5-15.6 mg/day 4
• Gender differences: women may require lower doses than men (7.0 mg vs 15.6 mg) 4

Pediatric Hypertension

• Initial dose: 0.05-0.1 mg/kg per day divided three times daily 4
• Maximum dose: 0.5 mg/kg per day 4

Important Considerations

First-Dose Phenomenon

• First-dose hypotension occurs in approximately 0.15% of patients (1 in 667) 2
• Risk reduction strategies:
  • Withhold diuretics for 1 day before starting prazosin
  • Take initial dose at bedtime
  • Start with recommended low dose (1 mg) 2
  • Monitor closely in patients with recent stroke (higher risk) 3

Concomitant Medications

• When adding diuretics or other antihypertensives:
  • Reduce prazosin dose to 1-2 mg three times daily
  • Retitrate as needed 1
• PDE-5 inhibitors:
  • Can cause additive hypotensive effects
  • Start PDE-5 inhibitors at lowest dose in patients taking prazosin 1

Response Patterns

• Two distinct response patterns have been observed:
  1. Marked BP reduction after first dose (52/30 mmHg), minimal pulse increase, requires lower maintenance dose 5
  2. Minimal BP reduction after first dose (14/13 mmHg), significant pulse increase, requires higher maintenance dose 5

Side Effects

• Most common: headache, dizziness, palpitations 6
• Usually mild and transient, lasting 1 day to 2 weeks 6
• Sexual dysfunction is uncommon 2
• Fluid retention may develop with long-term therapy (rare) 2

Efficacy

• Effective across all ranges of hypertension (mild, moderate, severe) 2
• Approximately 86% of patients achieve satisfactory blood pressure response 6
• 70% of patients respond to doses of 4 mg or less 6
• Obese patients may be more resistant to treatment effects 6

Prazosin dosing should be carefully monitored, especially during initiation, with particular attention to blood pressure response and orthostatic hypotension risk. The first dose should always be administered at bedtime to minimize the risk of syncope.