Captopril has no significant scavenging antioxidant activity in human plasma in vitro or in vivo.

1. Captopril has been reported to possess hydroxyl radical (OH.) and hypochlorous acid (HOCl) scavenging effects, which could contribute to its therapeutic activity in the clinical setting. 2. The objective of the present study was to determine whether therapeutically achievable captopril concentrations could augment antioxidant properties of human plasma and protect it against OH.- and HOCl-driven oxidant injury in vitro. Possible drug influences on systemic oxidative stress status in vivo were also investigated in subjects taking 50 mg captopril orally by measuring plasma and red blood cell peroxidation, as well as plasma protein thiols. 3. The results show that captopril is incapable of enhancing antioxidant properties of human plasma, of protecting it against specific oxidative attack and of decreasing systemic oxidant load in vivo. 4. The present data, therefore, do not support the contention of a beneficial action of captopril through systemic antiradical-antioxidant effects in human beings.