Population pharmacokinetics of mitoxantrone performed by a NONMEM method

To date, the pharmacokinetics of mitoxantrone (1,4-dihydroxy-5,8-bis[[2-[(2- hydroxyethyl)amino]ethyl]amino]anthraquinone) has been described either by an open two- or three-compartment model, showing high interindividual variability. In order to evaluate this variability, residual intraindividual variability, and measurement error, we carried out a population study. A sensitive HPLC method allowed analysis of blood samples drawn from 21 patients with breast cancer or acute nonlymphocytic leukemia. Individual data treatment (22 kinetics) using weighted nonlinear least squares regression confirmed the huge interindividual variability whatever the administration protocol of mitoxantrone: bi- or tri-exponential models fitted the data. The NONMEM population method used herein describes all concentration-time curves by a single three-compartment model, considering biphasic kinetics as fragmentary data. Residual intraindividual variability was 21.4%. Population mean values (+/- interindividual SD) of clearance, terminal half-life, and total volume of distribution were, respectively, 23.40 (+/- 10.76) L/h, 46.87 (+/- 12.18) h, and 385.49 (+/- 196.60) L. These results are of particular interest in clinical routines to calculate dosage regimens by Bayesian estimation methods.