LC–MS/MS assay for quantitation of enalapril and enalaprilat in plasma for bioequivalence study in Indian subjects

BACKGROUND Enalapril (EPL) is an angiotensin-converting enzyme inhibitor for the treatment of hypertension and chronic heart failure. Enalaprilat (EPLT) is an active metabolite that contributes to the overall activity of EPL. AIM To quantitate EPL along with its metabolite EPLT using LC-MS/MS, a bioanalytical method was developed and validated with tolbutamide in human plasma using a protein precipitation technique. RESULTS The sensitive and selective method has an LLOQ of 1 ng/ml with a linearity range of 1-500 ng/ml for both EPL and EPLT using 300 µl of plasma without any matrix effect. CONCLUSION Linearity, specificity, accuracy, precision and stability, as well as its application to the analysis of plasma samples after oral administration of 20 mg of EPL maleate in healthy volunteers demonstrate applicability to bioavailability/bioequivalence studies.