Nitrendipine and enalapril combination therapy in mild to moderate hypertension: Assessment of dose-response relationship by a clinical trial of factorial design

Hypertension is an important cardiovascular risk factor and the goal of its pharmacologic treatment is to reduce morbidity and mortality. Treatment is usually initiated with a low dose of a single agent and titrated to a higher dose as required. As many as 50% of patients require the addition of a second agent to achieve satisfactory blood pressure control. The aim of this study was to assess the dose-response relationship of nitrendipine and enalapril alone or in fixed combination in the treatment of mild to moderate hypertension. A total of 496 patients were enrolled in a multicenter, randomized, double-blind, factorial-design, parallel-group clinical trial comparing placebo, nitrendipine (5, 10, and 20 mg) and enalapril (5, 10, and 20 mg) alone or in combination. After a single-blind, 2-week placebo run-in period, 414 patients whose diastolic blood pressure ranged between 90-109 mm Hg were randomly assigned to a treatment group. The combination of nitrendipine and enalapril, particularly regimens including nitrendipine 20 mg and enalapril 5 or 10 mg, were significantly superior to both monotherapies; mean diastolic blood pressure reductions from baseline to last visit were -12.5 and -14.3 mm Hg, respectively. Response surface analysis provided further evidence that these combinations were optimal in terms of anti-hypertensive efficacy. All treatments were well tolerated and the incidence of adverse events did not differ significantly between groups. In summary, the anti-hypertensive efficacy of the combination was found to be superior to both monotherapies at any doses. The dose combination achieving the greatest blood pressure reduction was nitrendipine 20 mg and enalapril 10 mg.