- The final model was validated using nonparametric bootstrap analysis. Body surface area (BSA), pre-hydration, baseline serum creatinine and 24 h creatinine clearance rate were statistically significant covariates for distributional volume (V) and renal clearance (CL). Herein, is the first report of analysis of the importance of a series of patient factors on pharmacokinetics of MTX by one-compartment model. Using these data, we have established an efficient population pharmacokinetic model for MTX, which can be used to predict safe clinical application of MTX especially in children with ALL.