Demonstration of a S-methyl metabolite of captopril in patients undergoing chronic captopril therapy.

1. The formation of the S-methyl metabolite of captopril has been demonstrated for the first time in the urine of five patients receiving chronic captopril therapy. 2. Patients were studied following a 100 mg oral dose of captopril. 3. Excretion values for S-methylcaptopril were 0.66 mg and 0.31 mg at 0-3 h and 3-6 h postdose. Captopril excretion was at these two collections 15.5 mg and 2.3 mg, respectively.