Vincristine disposition in children with acute lymphoblastic leukemia.

Vincristine (VCR) has been widely used to treat childhood malignancies for over thirty years, but its plasma disposition has not yet been well-defined. Therefore, we conducted a pharmacokinetic study of VCR in 17 children with acute lymphoblastic leukemia (ALL) receiving the first dose of VCR. A new high-performance liquid chromatographic assay was used for the measurement of VCR in plasma. A two-compartment pharmacokinetic model was fit to the data by nonlinear least-squares regression. Estimated pharmacokinetic parameters were highly variable; mean (S.D.) volume of distribution at steady-state was 360 (176) L.m-2; total body clearance was 431 (238) ml.min-1.m-2, and elimination half-life was 823 (390) min. These results were compared to data from eight adults with lung cancer. Mean volume of distribution in adults and children were similar, but VCR clearance was significantly larger in children (P = 0.01), resulting in a significantly longer elimination half-life in the adults (P < 0.01). We conclude that administration of a standard dosage of VCR to children with ALL results in a highly variable systemic drug exposure, which may have implications for the oncolytic effect and/or toxicity in individual patients. Comparison of data from children and adults suggests that VCR elimination rate is a function of age; this could account for more severe neurotoxicity in older patients. However, it cannot be excluded that differences between the children and adults may be due to other variables than age. Future studies should focus on the possible influence of multidrug resistance modulating agents on VCR pharmacokinetics and on pharmacokinetic-pharmacodynamic relationships in individual patients.