This is the first model to describe the pharmacokinetics of doxorubicin in children, with a specific focus on infants and children aged <3 years. The lower CL in younger children should be considered together with the pharmacodynamics, especially the cardiotoxicity, when selecting the dose for future protocols.

A four-compartment NONMEM(®) model for doxorubicin and doxorubicinol adequately described the plasma concentrations in adults and children (>3 years). No pronounced effects of age on the clearance of doxorubicin or doxorubicinol were found, and the analysis did not support the modification of the dosing strategies presently used in children and adults.

Under the described conditions, the push-pull method delivered the same results as the discard method to prevent sample dilution. To avoid contamination in plasma samples, development of standardized sampling procedures seems to be essential and feasible.

The choice of the infusion apparatus, standardized infusion systems, and standardized operating procedures for drug administration are important when performing postmarketing PK analyses in multicentric studies.

Doxorubicin is a key component of a number of treatment regimens used in paediatric oncology, despite the very limited pharmacology data on which current dosing regimens are based. We conducted a multicentre, multinational phase II pharmacokinetic study investigating age-dependency in the clearance of doxorubicin in children with solid tumours and leukaemia. The study was funded under the Framework Program 7 of the European Commission. 101 patients treated with doxorubicin according to a tumour-specific national or European therapeutic trial were recruited to the study, with a particular focus on children less than 3 years. Absolute doses of doxorubicin ranged from 2.4 to 57 mg, administered, with infusion durations ranging from 0.25 to 24 hours. Samples were collected after 2 administrations, with 5 samples collected in children &lt;3yrs and 8 samples in children ≥3yrs. Doxorubicin and its major metabolite doxorubicinol were measured in plasma using a validated HPLC-fluorescence assay with a limit of quantification of 2 μg/L for each analyte. Markers such as troponin T and natriuretic peptides were measured to evaluate as clinical indicators of cardiotoxicity. Data were analysed using a population pharmacokinetic approach, including pharmacogenetic covariates. Data were available from all but 5 patients, with samples lost due to withdrawn consent, analytical issues or sample stability related to sample transport. A three compartment model was sufficient to characterize the pharmacokinetics of doxorubicin, with a further compartment to describe those of the major metabolite doxorubicinol. All parameters of the population model were scaled to body surface area. Age dependence of doxorubicin clearance was demonstrated, with children less than 3 years having a lower clearance (21.1±5.8 l/h/m2) than older children (26.6±6.7 l/h/m2) (p=0.0004), even after correcting for body weight. No other patient-related covariate, including liver function, was found to influence the parameters of the model. While the model provided a good fit to the doxorubicinol data, no covariate was identified which influenced the parameters of the metabolite model. Pharmacogenetic variants, including those in transporters and drug metabolizing enzymes, had little influence on pharmacokinetic parameters. Likewise, pharmacokinetics had only limited impact on markers of cardiotoxicity such as troponins or on measured cardiac function. This study yields new pharmacokinetic data on doxorubicin pharmacokinetics in very young patients, suggesting that lower doses may be appropriate in children less than 3 years. The data presented her may be useful for refining dosage regimens in this patient group. Citation Format: Alan V. Boddy, Nicolas Andre, Gianni Bisogno, Joachim Boos, Maurizio D'Incalci, Nina Kontny, Miriam Krischke, Swantje Voeller, Georg Hempel. Age dependence of doxorubicin pharmacokinetics in pediatric cancer patients; results of an FP7-funded clinical study. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4625. doi:10.1158/1538-7445.AM2014-4625