Population pharmacokinetics of intravenous busulfan in children: revised body weight-dependent NONMEM® model to optimize dosing.

PURPOSE: We developed a new population pharmacokinetic (PopPK) model for intravenous (i.v.) busulfan in children to evaluate the optimal method to personalize its dosing without concentration-time data.
METHODS: PopPK analyses were done with NONMEM® 7.2. First, a model from Trame et al. was evaluated using an external dataset consisting of 24 children. Second, a revised model was built in a separate dataset of 82 children. Model evaluation was performed by using a standardized visual predictive check (SVPC) procedure and a bootstrap analysis (internal evaluation) and by comparison to an external dataset (external validation).
RESULTS: The final model included body surface area (BSA) as an exponential function on volume of distribution (V) and actual body weight (ABW) as an allometric function on clearance (CL). The dosing nomogram for every 6 h administration derived from the final model is: dose[mg]=target AUC[mg×h/L]×3.04L/h×(ABW/16.1)0.797. Compared to other dosing strategies, differences were observed for the very small and obese patients.
CONCLUSIONS: We revised our prior dosing nomogram after validation in a separate cohort of children. This dosing nomogram can be used to personalize i.v. busulfan doses without concentration-time data, but an additional prospective evaluation in the very small and obese children is needed.