Effect of 8-Week Combination Therapy with an Extended-Release α1-Blocker (Bunazosin or Doxazosin) in Inadequate Responders to an Angiotensin II Antagonist (Valsartan) in Patients with Stage 1 or 2 Essential Hypertension

Background: Given the favorable impact of alpha(1)-blockers on lipid and glucose metabolism, this study was designed to compare the efficacy of two extended-release alpha(1)-blockers (bunazosin and doxazosin) as an add-on treatment in subjects with stage 1 or 2 essential hypertension which was inadequately controlled by valsartan 80 mg/day. Methods: After a 5-week treatment of valsartan monotherapy, subjects with inadequately controlled hypertension were randomized to receive either extended-release bunazosin (n = 47) or doxazosin (n = 46) after breakfast for 8 weeks. Office sitting blood pressure (BP), 24-hour ambulatory BP, and metabolic profiles were measured at baseline, start of study drug, and study end. Results: In the intention-to-treat population (n = 93), the average daily doses of bunazosin and doxazosin were 2.8 mg and 3.6 mg, respectively. The two add-on treatments achieved significant and similar BP reductions from monotherapy (bunazosin, 13.2/9.3 mmHg; doxazosin, 9.2/8.5 mmHg, all p<0.001). However, in patients with stage 2 hypertension, patients randomized to the bunazosin group, compared to those in the doxazosin group, achieved a significantly greater reduction in sitting systolic BP (14.4 +/- 8.1 vs. 6.6 +/- 13.8 mmHg, p = 0.015). In addition, patients who received bunazosin had significant changes in night-day systolic and diastolic BP ratios compared with those who received doxazosin (-0.02 vs. 0.02, p = 0.04 and 0 vs. 0.04, p = 0.04). No significant changes in metabolic profiles were observed in both add-on groups. Both drugs were well-tolerated, but adverse events related to the study drugs were marginally more frequent in the doxazosin group than in the bunazosin group (20% vs. 6%, p = 0.058). Conclusions: Both extended-release bunazosin and doxazosin were well-tolerated and similarly effective as add-on therapy in hypertensive patients uncontrolled by valsartan monotherapy. However, add-on treatment with bunazosin seemed to be associated with favorable night-day BP ratio and greater sitting systolic BP reductions in stage 2 hypertensive patients.