Converting from Amlodipine 5mg to Doxazosin
Stop amlodipine abruptly and start doxazosin 1mg once daily in the morning or evening, then titrate upward every 1-2 weeks based on blood pressure response, monitoring closely for at least 6 hours after each dose adjustment. 1
Direct Conversion Protocol
There is no direct dose equivalency between amlodipine and doxazosin—these agents work through completely different mechanisms (calcium channel blockade vs. alpha-1 adrenergic blockade), so you must start doxazosin at its initial recommended dose regardless of the amlodipine dose. 1, 2
Discontinue amlodipine 5mg immediately without tapering, as calcium channel blockers do not require gradual withdrawal. 3
Start doxazosin at 1mg once daily (either morning or evening) on the same day you stop amlodipine, as this is the FDA-mandated initial dose for hypertension to minimize first-dose hypotensive effects. 1
Titration Schedule
Monitor blood pressure for at least 6 hours after the first dose and after each dose increase, as doxazosin can cause significant orthostatic hypotension, particularly with initial dosing. 1
Titrate doxazosin by doubling the dose every 1-2 weeks based on blood pressure response: 1mg → 2mg → 4mg → 8mg → 16mg once daily, with a maximum dose of 16mg daily for hypertension. 1
Most patients achieve adequate blood pressure control at 2-8mg daily, with mean effective doses around 2.4-13mg in clinical trials. 4, 5
Expected Blood Pressure Response
Doxazosin provides 24-hour blood pressure control with once-daily dosing, with mean reductions of approximately 23/13 mmHg in supine position and 24/12 mmHg in standing position at therapeutic doses. 4, 3
Full antihypertensive effect develops gradually over 1-2 weeks at each dose level, so allow adequate time before further titration. 2
Doxazosin is equally effective in elderly and younger patients, and shows similar efficacy in Black and Caucasian populations. 2
Critical Monitoring Parameters
Check both sitting and standing blood pressures at each visit, as doxazosin can cause orthostatic hypotension, particularly in the first few weeks of therapy. 1, 4
Reassess blood pressure within 2-4 weeks after starting doxazosin and after each dose adjustment to determine if further titration is needed. 6
If therapy is interrupted for several days, restart at the initial 1mg dose and retitrate upward, as the protective adaptation to first-dose effects is lost. 1
Important Clinical Considerations
Doxazosin is generally well-tolerated, with side effects typically mild to moderate in severity and often resolving with continued therapy. 2, 4
Common adverse effects include dizziness, fatigue, and headache, which are usually transient and decrease with continued use. 2, 5
Doxazosin favorably affects lipid profiles, increasing the HDL/total cholesterol ratio compared to placebo, which may provide additional cardiovascular benefit. 2
Why This Conversion May Not Be Ideal
Current hypertension guidelines do not recommend alpha-blockers like doxazosin as preferred antihypertensive agents unless there are compelling indications such as benign prostatic hyperplasia. 6
If blood pressure remains uncontrolled on amlodipine 5mg alone, guideline-recommended approaches include adding an ACE inhibitor/ARB or thiazide diuretic rather than switching to doxazosin. 6
Combination therapy with amlodipine plus an ACE inhibitor/ARB or thiazide provides superior cardiovascular outcomes compared to monotherapy with alternative agents. 6
If switching is necessary due to amlodipine intolerance, consider alternative first-line agents (ACE inhibitors, ARBs, or thiazide diuretics) before doxazosin unless the patient has BPH requiring treatment. 6, 1