Assay of 6-mercaptopurine and its metabolites in patient plasma by high-performance liquid chromatography with...

A reversed-phase high-performance liquid chromatography (HPLC) method was developed to determine 6-mercaptopurine (MP) and seven of its metabolites (6-thioguanine, 6-thioxanthine, 6-mercaptopurine riboside, 6-thioguanosine, 6-thioxanthine riboside, 6-methylmercaptopurine and 6-methylmercaptopurine riboside) simultaneously in human plasma. A volume of 100 microl of plasma was used. Protein was removed from the sample by a simple and easy ultrafiltration step and ultrafiltrate was directly injected onto the HPLC system. Analytes were detected and confirmed with a diode-array detector before quantitation at 295 and 330 nm. The limit of detection for the analytes ranged from 20 to 50 nM. For the majority of patients receiving a 1 g/m2 MP intravenous infusion, MP and all metabolites except 6-thioguanine and 6-methylmercaptopurine riboside were present. This method serves as useful tool to characterize pharmacokinetics and pharmacodynamics of MP in oncology patients, and the small volume of plasma lends itself to pediatric studies.