Mercaptopurine Bioavailability

To the Editor: On the basis of pharmacokinetic data, Zimm et al., 1 have questioned whether an optimal amount of mercaptopurine is currently being given in maintenance chemotherapy regimens for acute lymphoblastic leukemia (April 28, 1983, issue). They suggest that giving mercaptopurine intravenously, rather than orally, and monitoring the dose by determining blood levels might increase the effectiveness of this agent and reduce the relapse rate in acute lymphoblastic leukemia, which is still about 50 per cent. 2 , 3 The biochemical pharmacology of mercaptopurine may be more important than the pharmacokinetic data. Mercaptopurine is a prodrug that becomes active only after conversion to . . .