Simultaneous high-performance liquid chromatographic analysis of omeprazole and its sulphone and sulphide metabolites in human plasma and urine.

Omeprazole, a substituted benzimidazole which suppresses gastric acid secretion, and its sulphone and sulphide metabolites were simultaneously measured in human plasma and urine using a selective, reversed-phase, high-performance liquid chromatographic method with a sensitivity of 5 ng/ml for omeprazole, 30 ng/ml for omeprazole sulphone, and 50 ng/ml for omeprazole sulphide. The coefficients of variation for within-day assays were 4.4, 7.5, and 17.5%, respectively. In a pilot pharmacokinetic study, 40 mg of omeprazole (encapsulated enteric-coated granules) were administered to two healthy volunteers. Peak plasma concentrations for omeprazole of 240 and 520 ng/ml, and for omeprazole sulphone of 320 and 400 ng/ml, were reached between 3 and 4 h post-dose. Omeprazole concentrations fell rapidly with apparent half-lives of about 40 min, and concentrations of both omeprazole and the sulphone metabolite were below the minimal detectable level by 6-8 h. Omeprazole sulphide could not be detected in this study.