Clinically additive effect between doxazosin and amlodipine in the treatment of essential hypertension

The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure has reported that combinations of low doses of antihypertensive agents from different classes may provide additional antihypertensive efficacy and minimize the likelihood of dose-dependent adverse effects. Doxazosin and amlodipine, alone and in combination, were compared for efficacy in reducing blood pressure (BP) in 75 patients with predominantly moderate (Stage 2) hypertension. This was a double-blind, randomized, crossover study. After a 2-week washout period, patients in group A (n = 37) received amlodipine 10 mg and patients in group B (n = 38) received doxazosin 4 mg for 6 weeks. All patients then received reduced-dose combination therapy (amlodipine 5 mg and doxazosin 2 mg) for 6 weeks. Subsequently, patients received 6 weeks of monotherapy with the alternate medication (group A received doxazosin 4 mg and group B received amlodipine 10 mg). During both monotherapy periods, doxazosin and amlodipine significantly reduced systolic and diastolic BP (P< .001 v baseline). BP further decreased with combination therapy (P< .01 v monotherapy). The percentage of patients with Stage 2 hypertension who achieved a target BP of < 140/< 90 mm Hg increased from 78% with monotherapy to 94% with combination therapy. Fewer adverse effects were observed during combination therapy. It is concluded that there is an additional fall in blood pressure when reduced doses of doxazosin and amlodipine are used in combination for the treatment of hypertension, suggesting that doxazosin should be considered as an effective add-on treatment to calcium-channel blockers.