Serum creatinine and creatinine clearance for predicting plasma methotrexate concentrations after high-dose methotrexate chemotherapy for the treatment for childhood lymphoblastic malignancies

Monitoring of plasma methotrexate (MTX) concentrations allows for therapeutic adjustments in treating childhood acute lymphoblastic leukemia (ALL) or non-Hodgkin lymphoma (NHL) with high-dose MTX (HDMTX). We tested the hypothesis that assessment of creatinine clearance (CrCl) and/or serum Cr may be a suitable means of monitoring plasma MTX concentrations. All children in the study had ALL or NHL, were in complete remission, and received HDMTX (3 or 5 g/m2)+leucovorin. Plasma MTX concentrations were measured at 24, 48, and 96 h. CrCl was determined at 24 and 48 h. Correlations between 24- and 48-h plasma MTX concentrations and CrCl and serum Cr concentrations were determined. CrCl and serum Cr concentrations were compared over time between children who had delayed and non-delayed MTX elimination. A total of 105 children were included. There were significant negative correlations between CrCl at 24 and 48 h and plasma MTX concentrations at 24 (both p