Large interindividual variations in the pharmacokinetics of oral 6-mercaptopurine in maintenance therapy of children with acute leukaemia and non-Hodgkin lymphoma.

The concentrations of 6-mercaptopurine were studied in plasma and red blood cells from 10 children with acute leukaemia or non-Hodgkin lymphoma receiving oral maintenance therapy. The doses varied between 25 and 79 mg/m2 body surface once daily. Large interindividual differences were found in the concentrations both in plasma and in red blood cells. There was no clear relationship between the dose administered and the concentrations obtained. However, in each patient the concentrations in plasma and in red blood cells were very similar. In most patients, the peak concentrations were reached 1-2 hours after dose intake and the concentrations then declined with half-lives less than 1 hour. Further studies are necessary to evaluate the potential value of drug level monitoring in optimizing treatment with oral 6-mercaptopurine.