6-Methylmercaptopurine (6-MMP) is a metabolite of the purine synthesis and interconversion inhibitor 6-mercaptopurine .1 It is formed from 6-MP via methylation by thiopurine S-methyltransferase. Levels of 6-MMP are increased in patients with altered thiopurine metabolism and associated with therapeutic resistance to 6-MP.2
1.Rieder, M.J., and Carleton, B.Pharmacogenomics and adverse drug reactions in childrenFront. Genet.578(2014) 2.van Egmond, R., Chin, P., Zhang, M., et al.High TPMT enzyme activity does not explain drug resistance due to preferential 6-methylmercaptopurine production in patients on thiopurine treatmentAliment. Pharmacol. Ther.35(10)1181-1189(2012)