Biotransformation studies of di-acid angiotensin converting enzyme inhibitors

The biotransformation of di-acid inhibitors of angiotensin converting enzyme was studied in the urine of rats using gas chromatography/mass spectrometry. It was found that after oral administration (10 mg/kg) of enalapril significant amounts (9.2%) of a hydrolytic metabolite of enalaprilat were excreted in urine which was identified as 2-N-alanyl-4-phenylbutanoic acid. This metabolite was present only in trace concentrations in urine after intravenous administration. This pathway was not present, however, with either ramipril or perindopril suggesting that the amide bond in these newer inhibitors is more resistant to hydrolysis than for enalapril. Glucuronidase hydrolysis of urine obtained from rats dosed with either enalapril, ramipril or perindopril indicated the absence of glucuronidate conjugates of these inhibitors in rat urine.