Thiopurine metabolism. 6-MP, mercaptopurine; IMP, inosine monophosphate; IDP, ioinosine diphosphate; ITP, ioinosine triphosphate; GMP, guanosine monophosphate; GDP, guanosine diphosphate; GTP, guanosine triphosphate; XO, xanthine oxidase; HPRT, hypoxanthine phosphoribosyltransferase; TPMT, thiopurine methyltransferase; IMPD, inosine monophosphate dehydrogenase; GMPS, guanosine monophosphate synthetase; ITPA, inosine triphosphate pyrophosphatase