Prazosin Dosing Frequency
Prazosin should be taken 2 to 3 times daily, with the FDA-approved regimen starting at 1 mg two or three times per day and titrating to maintenance doses of 6-15 mg daily in divided doses. 1
Standard Dosing Schedule
Initial Dosing
- Start with 1 mg administered 2-3 times daily 1
- The first dose should be given at bedtime to minimize first-dose hypotension 1, 2
- This "first-dose phenomenon" causes severe postural hypotension and can be eliminated by starting at 0.5 mg before retiring to bed 2
Maintenance Dosing
- Most patients require 6-15 mg total daily dose divided into 2-3 administrations 1
- The maximum effective dose is typically 20 mg daily in divided doses, though some patients may benefit from up to 40 mg daily 1
- After initial titration, some patients can be maintained on twice-daily dosing 1
Dosing Frequency Rationale
- Prazosin has an elimination half-life of approximately 2.5 hours, necessitating multiple daily doses for sustained blood pressure control 3
- Twice-daily dosing provides adequate 24-hour blood pressure control in most patients 4
- The JNC-7 guidelines confirm prazosin requires 2-3 times daily administration for hypertension management 5
Context-Specific Dosing
For PTSD-Related Nightmares
- Bedtime dosing is standard, with mean effective doses ranging from 3.1 mg to 15.6 mg (higher in men) 5
- Some protocols include a mid-morning dose in addition to bedtime administration for active-duty soldiers 5
- Effective doses for nightmares ranged from 1-15 mg in clinical trials 5
When Combined with Other Antihypertensives
- Reduce prazosin to 1-2 mg three times daily when adding diuretics or other agents, then retitrate 1
- The American College of Cardiology recommends prazosin 2-20 mg per day in 2-3 divided doses when used for hypertension with concomitant BPH 6
Critical Dosing Considerations
Titration Strategy
- Increase doses slowly to reach the total daily target of 20 mg in divided doses 1
- Limit dose increments to 0.5 mg, beginning late in the evening to avoid orthostatic hypotension 2
- Doses above 20 mg rarely increase efficacy, though occasional patients benefit from up to 40 mg daily 1
Special Populations
- In chronic renal failure, elimination half-life is prolonged and free drug fraction increases, requiring cautious titration 3
- In congestive heart failure, pharmacokinetics are altered with longer half-life and increased peak concentrations 3
- Elderly patients are more susceptible to orthostatic hypotension and require careful blood pressure monitoring 6, 7
Common Pitfalls to Avoid
- Never start with doses higher than 1 mg to prevent severe first-dose syncope 1, 2
- Do not assume once-daily dosing is adequate despite the convenience—prazosin's short half-life requires multiple daily doses for consistent effect 1, 3
- Monitor standing blood pressure closely after dose initiation or increases, as orthostatic hypotension is the most frequent side effect 2, 6
- When discontinuing prazosin, abrupt cessation is generally safe as it does not cause withdrawal phenomena, unlike clonidine 7