Inhibition of angiotensin-converting enzyme with libenzapril in normotensive males

The effect of intravenous (i.v.) libenzapril was studied in six healthy males by administering i.v. angiotensin I (AI) administered in stepwise increments of 20 ng/kg/5 min until the subjects' systolic blood pressure (SBP) had increased 20-30 mm Hg above baseline. The mean baseline infusion of 63 ng/kg/5 min resulted in a significant (P < 0.05) increase in the ratio of AII to AI plasma levels from 0.52 +/- 0.46 to 7.92 +/- 4.48 and a SBP increase of 120 +/- 7.1 to 147 +/- 5.6. Within 15 minutes of starting the 1-mg infusion of libenzapril over 1.5 hours, the AII/AI ratio decreased to baseline values, and the SBP had returned to baseline in 1 hour. Repeat AI challenges at 3.5 and 5 hours postdose did not increase SBP significantly. Even the 6.5-hour challenge demonstrated only a slight increase in SBP, with an AII/AI ratio of 0.26. At 24 hours, SBP was only 40% of the baseline response, demonstrating that libenzapril is a potent long-acting ACE inhibitor.