Clinical efficacy and tolerability of alpha-blocker doxazosin as add-on therapy in patients with hypertension and impaired glucose metabolism

Abstract

Background and aim: The aim of this trial was to evaluate the effect of doxazosin as add-on therapy in patients with hypertension not adequately controlled on current antihypertensive therapy, and impaired glucose metabolism. The effect of doxazosin administered as add-on therapy was to be considered significant both from clinical and statistical viewpoints if the proportion of patients with adequate control of blood pressure (BP<130/85 mmHg) would be at least 30% after 16 weeks of combined therapy.

Method and results: It was an open, multicenter phase IV study, lasting 19 weeks: 3-week qualifying/placebo run-in period+16-week dose titration/add on therapy period, involving 264 out-patients (158 m and 106 f; mean age+/-SD: 60.9+/-8.6 years; mean BMI+/-SD: basal 29.5+/-5.1, final 30.2+/-4.6) with blood pressure still >130/85 mmHg in spite of the antihypertensive treatment (ACE inhibitors 44%, AT II antagonists 21%, Ca antagonists 12%, other drugs 8%, polytherapy 15%) and affected by type 2 diabetes (n=219), impaired fasting glucose (IFG; n=16) or impaired glucose tolerance (IGT; n=29). Following a run-in, 3-week qualifying phase during which placebo was added to ongoing antihypertensive treatment, 16-week treatment with doxazosin was added at dosages from 1 up to 8 mg/day. Main outcome measures were: the percentage of patients with blood pressure <130/85 mmHg at the end of treatment; the effects of the combination therapy on glyco-lipidic metabolism: fasting plasma glucose, fasting insulin, glycated hemoglobin, insulin resistance (HOMA-R), plasma lipids; and the effect on the 10-year CHD risk (Framingham equation).

Results: 35% of patients were responsive (BP<130/85 mmHg) to add-on treatment with doxazosin (CI 90%: 30.3%-40.4%; P<0.05, stat. an. intention to treat). During the run-in phase with placebo, mean SBP/DBP (+/-SD) decreased from 155.6+/-13.2/91.8+/-6.8 mmHg (Week -3) to 151.9+/-12.9/90.1+/-7.2 mmHg (Week -1) and to 151.2+/-11.5/90.1+/-6.9 mmHg (Week 0). During add-on treatment with doxazosin, mean SBP/DBP (+/-SD) further decreased to 144.9+/-15.2/86.3+/-8.3 mmHg (Week 4), 139.7+/-15.3/83.4+/-7.9 mmHg (Week 8), 135.5+/-14.3/81.7+/-7.6 mmHg (Week 12) and 136.4+/-14.5/81.0+/-7.0 mmHg (Week 16). Overall, mean BP changes reached a plateau of about -15 mmHg (SBP) and -9 mmHg (DBP) after 16 weeks of treatment; at each visit the mean decreases from baseline were statistically significant. The following mean values of metabolic parameters were reduced during the study: fasting plasma glucose (-4.1mg/dl; -2.8%), fasting insulin (-2 microU/ml; -12.3%; P<0.05), glycated hemoglobin (-0.12%; -1.7%), HOMA-R (-1.03; -18.2%; P<0.05), total cholesterol (-1.85 mg/dl; -1.1%), LDL cholesterol (-1.35 mg/dl; -0.8%) and triglycerides (-5.64 mg/dl; -2.4%); mean HDL cholesterol increased (+1.79 mg/dl; +3.9%; P<0.01). At the end of study treatment, the percentage of patients with lab values returned within normal ranges, in comparison with basal values, was statistically significant (P<0.05) for the following parameters: fasting plasma glucose (6.3%), fasting insulin (7.5%), LDL cholesterol (6.0%). Ten-year CHD risk (+/-SD) decreased from 16.4+/-7.8% to 13.6+/-7.4% (final vs. basal: -2.87+/-3.9; -17%; P<0.01). Six patients (2.3%) reported 8 adverse drug reactions: dizziness (3), edema (2), headache (2), asthenia (1). In one out of these 6 patients, in whom doxazosin was associated to the ACE inhibitor quinapril, adverse reaction (peripheral edema) led to treatment withdrawal.

Conclusion: In patients not responsive to antihypertensive treatment and concomitantly affected by impaired glucose metabolism, achievement of target BP was obtained in more than one third of cases after 16-week add-on treatment with doxazosin. Changes in glyco-lipidic parameters and reduction of 10-year CHD risk observed during the study, although of moderate extent, confirm the overall favourable effect of antihypertensive combinations including doxazosin.