Population pharmacokinetics and exploratory pharmacodynamics of ifosfamide according to continuous or short infusion schedules: an n = 1 randomized study.

ABSTRACT

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * The optimal infusion duration for ifosfamide remains to be determined. * No differences according to time of infusion have been identified in traditional pharmacokinetic endpoints, such as area under the curve. * The impact on pharmacodynamics has never been modelled or correlated with pharmacokinetics. WHAT THIS STUDY ADDS * The pharmacokinetics and pharmacodynamics of ifosfamide and its main metabolites can both be modelled with no influence of infusion duration. * Pharmacodynamic modelling (renal and haematological toxicity) allows further simulations of new schedules with favourable toxicity profiles. AIMS: To model the pharmacokinetics and pharmacodynamics of ifosfamide and its key metabolites. The pharmacodynamic parameters included were renal toxicity and myelosuppression measured using urinary beta(2)-microglobulin (BMG) and absolute neutrophil count (ANC), respectively. METHODS: Seventeen patients were enrolled into an n = 1 randomized trial during two consecutive cycles of ifosfamide 9 g m(-2) during each cycle given by a 3 h or 72 h infusion. Data were analyzed using NONMEM. RESULTS: Ifosfamide and metabolite concentration-time profiles were described by a one-compartment open-model with auto-induction of clearance. BMG and ANC time-courses were related to ifosfamide concentration via indirect response models. CONCLUSIONS: This modelling allowed the simulation of weekly schedules of flat doses with favourable myelotoxic profiles.