Comparison of Efficacy of Spirapril and Enalapril in Control of Mild-to-Moderate Hypertension

The efficacy of spirapril, 6 mg once daily, was compared with enalapril, 5–20 mg once daily, in the control of mild-to-moderate hypertension in a placebo-controlled, parallel-group study. A total of 251 patients participated in the study, all of whom underwent a 4-week washout period on placebo. Thereafter, 100 patients were randomized to spirapril, 6 mg once daily, 101 patients to enalapril, 5–20 mg once daily, and 50 patients remained on placebo. Sitting diastolic blood pressure (DBP) and systolic blood pressure (SBP) were measured at 2-weekly clinic visits. Blood pressure profiles during peak and trough plasma drug concentrations (2–4 hours and 24 hours postdose, respectively) were determined at baseline and 4 and 8 weeks after starting the double-blind phase. Compared with placebo, treatment with both spirapril and enalapril resulted in significant reductions (p > 0.001) in DBP and SBP. DBP was reduced to a greater extent with spirapril than with enalapril both at peak (−17.4 mmHg vs. −14.8 mmHg) and trough (−14.7 mmHg vs. −12.4 mmHg). Thus, although the trough/peak DBP ratios for spirapril and enalapril were very similar (84% vs. 82%), actual reductions in DBP were different. Spirapril and enalapril treatment resulted in similar reductions in SBP at both peak and trough levels. Both drugs were well tolerated, and there were very few adverse events or changes in hematological or biochemical parameters during the study. In conclusion, spirapril, 6 mg once daily, as the initial and maintenance dose, is at least as effective and well tolerated as enalapril individually titrated.