Analytical Studies on Mepirizole and Its Metabolites. IV. Quantitative Determination of Mepirizole in Human Serum by Mass Fragmentography, and Isotope Effect on Drug Metabolism

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Mass fragmentographic determination of mepirizole in human serum was carried out with the aid of its deuterium labeled compound as the internal standard. Maximal serum level was observed at 60 minutes after oral administration. Simultaneous observation of isotope effect on metabolic rate revealed that serum level of mepirizole deuterated at the methyl group of the pyrazole ring was slightly higher than that of mepirizole, but the isotope effect was observed on the formation of the metabolites.