[New aspects of the determination of blood methotrexate levels in leukemic children].

Serum and CSF concentrations after medium dosage of methotrexate (MTX; 500 mg/m2 - 1,000 mg/m2) have been determined by an enzymatic assay during 142 infusions in children with ALL. If the dose of MTX was 500 mg/m2 MTX concentrations in CSF were under 10(-6) M/l in 40% of the treatments but only in 22%, when the dose was increased to 1,000 mg/m2. The systemic clearance of MTX was found to be increased significantly by the 2nd MTX treatment in children who relapsed thereafter. Such a phenomenon was not observed in children who continued in remission. The relapse free survival of children, whose MTX-clearance remained constant by the 2nd MTX treatment was significantly longer. No serious MTX toxicity has been observed in our patients.