Analysis of 6-mercaptopurine in serum or plasma using high performance liquid chromatography

The analysis of 6-mercaptopurine (6-MP) by a rapid, sensitive, and specific high performance liquid chromatographic assay is described. This method does not require any derivatization and allows for direct quantitation of the drug. Only 200 microliters of serum or plasma is needed, and concentrations as low as 10 ng/ml can be reliably quantitated. Analytical recoveries of 83% for 6-MP and 71% for the internal standard, 6-thioguanine, are obtained. Between-day precision studies at three plasma concentrations of 6-MP produce a mean coefficient of variation of 7.2%. This assay will be clinically useful for pharmacokinetic studies of 6-MP in patients in remission of acute lymphoblastic leukemia.