PHARMACOKINETICS OF MERCAPTOPURINE - PLASMA DRUG AND RED-CELL METABOLITE CONCENTRATIONS AFTER AN ORAL DOSE

Measurement of red cell 6-mercaptopurine (MP) derived 6-thioguanine nu cleotide (TGN) and methylmercaptopurine metabolites (MeMPs) can be use d to monitor therapy in children who are administered MP for childhood lymphoblastic leukemia. Red cell TGNs are not influenced by the time of blood sampling in relation to the last MP dose. The purpose of this study was to find out whether the same is true for the MeMPs. Plasma MP and red cell MP metabolite pharmacokinetics were studied in seven c hildren immediately before and for 4 hours after a protocol standardiz ed dose of MP. Duplicate blood samples were taken, one was processed i mmediately whereas one was left at an ambient temperature for 24 hours . The variation in TGN and MeMP metabolites over the 0- to 4-hour peri od (10 time points per child) was within the error of the assays used. The coefficients of variation for the TGNs ranged from 2.7% to 7% and for the MeMPs, 4% to 10.7%. There was no difference in the TGN and Me MP concentrations measured when the blood samples were left for 24 hou rs. If a child takes a MP tablet immediately before a clinic appointme nt, it has no major influence on MeMP measurements.