[Clinical pharmacology of enalapril]

Enalapril is an inhibitor of the converting enzyme which transforms angiotensin I into angiotensin II, an octapeptide with pharmacological properties uniformly tending to increase blood pressure. The enalapril molecule is not active until it has been hydrolyzed into enalaprilic acid in the liver. This acid induces a very strong (85-95%), very early (maximum at 2 hours) and long lasting (20% at 72 hours) blockade of the angiotensin-converting enzyme, resulting in a paralleled fall in systolic and diastolic blood pressure. The fall begins with a 2.5 mg dose of the drug, is maximum with 10 mg and is not increased by higher doses. No tachyphylaxis has been observed with prolonged administration. The fall in blood pressure is due to reduction of peripheral resistance, without changes in heart rate and cardiac output. There is no sodium retention. The two main pharmacokinetic features of the drug are its very long half-life and the 100% urinary excretion of the active metabolite. The drug can be taken as a single dose at any moment of the day. The only known interaction is with propranolol, which reduces by one-third the bioavailability of enalapril. Side-effects are uncommon and mild.