How long after stopping doxazosin can Flomax (tamsulosin) be started?

Switching from Doxazosin to Tamsulosin (Flomax)

Patients should wait at least 24 hours after stopping doxazosin before starting tamsulosin (Flomax) to minimize the risk of hypotensive effects from overlapping alpha-blocker activity. 1

Recommended Switching Protocol

The recommended protocol for transitioning between these alpha-blockers is:

1. Day 1: Take the last dose of doxazosin
2. Day 2: No alpha-blocker (24-hour washout period)
3. Day 3: Begin tamsulosin therapy at 0.4 mg once daily 1, 2

This washout period is necessary because doxazosin has a half-life of approximately 22 hours. After 24 hours, blood levels will have decreased significantly, reducing the risk of additive hypotensive effects when starting tamsulosin 1.

Administration Guidelines for Tamsulosin

When starting tamsulosin:

• Take 0.4 mg once daily, approximately 30 minutes after the same meal each day 2
• The first dose should be taken at bedtime to minimize potential orthostatic hypotension 1
• Do not crush, chew, or open the capsules 2
• For patients who don't respond to the 0.4 mg dose after 2-4 weeks, the dose can be increased to 0.8 mg once daily 2

Special Considerations and Precautions

Exercise particular caution when switching between alpha-blockers in:

• Elderly patients
• Patients with cardiovascular comorbidities
• Patients with history of syncope or orthostatic hypotension
• Patients taking other medications that may lower blood pressure 1

Monitoring Recommendations

During the transition period and first week after switching:

• Monitor for symptoms of hypotension (dizziness, lightheadedness)
• Check blood pressure in both sitting and standing positions at follow-up visits 1
• Be alert for any signs of cardiovascular complications

Potential Risks

The main risk when switching between alpha-blockers is hypotensive effects. Research has shown that the incidence of hypotension is generally low when proper switching protocols are followed 3. However, some patients may experience:

• Orthostatic hypotension
• Dizziness
• Syncope in rare cases 1, 3

Common Pitfalls to Avoid

1. Overlapping medications: Never start tamsulosin while still taking doxazosin
2. Inadequate monitoring: Failure to monitor for hypotensive symptoms during transition
3. Improper dosing: Starting with too high a dose of tamsulosin
4. Ignoring drug interactions: Be aware of other medications that may potentiate hypotension

Following these guidelines will help ensure a safe transition from doxazosin to tamsulosin while minimizing the risk of adverse effects.