Comparison of the free radical scavenging activity of captopril versus enalapril: a three month in vivo study in hypertensive diabetic patients.

Lipid peroxides and fluorescent serum proteins, possible markers of free radical activity, are increased in diabetic patients, particularly those with angiopathy. Captopril, an angiotensin converting enzyme (ACE) inhibitor, scavenges free radicals in vitro independently of ACE inhibition. This is probably due to the presence of a sulphydryl group which is not present in other ACE inhibitor drugs. We have compared the effects of captopril and enalapril on free radical activity in thirty-two diabetic subjects with hypertension (BP greater than 160/95 mmHg). After a three week run-in period on no antihypertensive therapy, patients were randomly allocated to receive captopril or enalapril, the dose titrated according to BP response. After three months, BP was well controlled in both groups and glycaemic control unchanged. Both drugs were associated with a reduction of fluorescent IgG (captopril:Baseline [BL] 0.564 vs. 12 weeks [w] 0.428, P less than 0.05, enalapril:BL 0.603 vs. 12w 0.422 P less than 0.05) and thiobarbituric acid reactive material (captopril:BL 2.35 nmol MDA vs. 12w 1.46 nmol, P less than 0.05, enalapril:BL 2.44 nmol vs. 12w 1.72 nmol, P less than 0.01). In contrast to in vitro studies, there was no significant difference between the drugs when used in therapeutic doses, questioning a hypothesised advantage of captopril over enalapril.