Acute cardiovascular effects of the concurrent administration of enalapril, prazosin or amlodipine in healthy Nigerians

Abstract

The acute circulatory effects of the combination of prazosin 1 mg, enalapril 10 mg or amlodipine 5 mg were evaluated and compared in placebo controlled, randomised, double blind, latin-square, cross-over study in 8 normotensive healthy Nigerians. Supine and erect blood pressure were reduced by the active treatment combinations ( F = 8.8, P = 0.0006, analysis of variance). In all, the onset of blood pressure fall was within 2 h, with a peak reduction at 4–6 h and persisting for at least 12 h. The combination of converting enzyme inhibitor and alpha blocker, however, caused a significantly greater hypotensive action than the other combinations ( P < 0.05, analysis of variance). There was a modest reflex tachycardia in the erect position on all treatments ( P = 0.008). Cardiac autonomic reflexes or left ventricular echocardiographic indices were unaffected by the drug combinations. The haemodynamic effect of enalapril plus prazosin combination, which separately cause little hypotensive effect in Africans, may reflect an important pharmacodynamic interaction between α 1 and angiotensin II vascular receptors. All combinations lower blood pressure and warrant further study in Nigerian hypertensives. However, the enalapril plus prazosin combination caused the greatest blood pressure fall, and caution is indicated during their concurrent use, owing to enhanced first dose hypotension.