Disposition of captopril in normal subjects

The disposition of Captopril, an angiotensin‐converting enzyme inhibitor with antihypertensive properties, was studied in 10 normal male subjects after a single 100‐mg tablet of 35 S‐labeled drug. Average absorption parameters for unchanged Captopril in blood were T max 0.93 ± 0.08 hr and C max 800 ± 76 ng/ml. For total radioactivity in blood the values were T max 1.05 ± 0.08 hr and C max 1,580 ± 90 ng/ml (as Captopril equivalents). Because of the curvilinearity of the semilogarithmic plots of blood concentrations of Captopril: time, elimination half‐life (t½) of unchanged drug could not be determined. At 1 hr unchanged Captopril accounted for about 52% of total radioactivity in blood, and the dimeric disulfide metabolite of Captopril accounted for about 10%. In the first 5 days after dosing, an average of about 68% of the radioactive dose was recovered in urine and 18% in feces. The distribution of radioactivity in the first 24‐hr urine sample (66% of the dose) was 58% Captopril (38% of dose), 2% Captopril disulfide (1.5% of dose), and 40% unidentified polar metabolites (26% of dose). Clinical Pharmacology and Therapeutics (1980) 27, 636–641; doi: 10.1038/clpt.1980.90