Preoperative high-dose methotrexate (HD-MTX) with folinic acid (leucovorin) rescue is still a mainstay in the treatment of osteosarcoma. This anticancer agent is characterized by a narrow therapeutic index and wide interpatients variability. To ensure effective and safe administration of HD-MTX, we had earlier developed an adaptive-dosing schedule with a feedback strategy. In our institute, the MTX dosage was tailored according to individual pharmacokinetics parameters, determined in real time both from two blood samples (3.5 and 4.5 h) and from Bayesian population parameters. Up to 20 g of MTX was safely administered as 8-h infusions. Low MTX elimination rate has, however, been reported in 15-20% of the patients, and forecasting the MTX elimination phase and the management of leucovorin rescue is still a challenging issue in clinical oncology. This study aims at identifying the clinical or biological covariates related to impaired MTX clearance, and at validating a new limited sampling strategy (LSS), allowing for the accurate prediction of the MTX terminal elimination phase. This retrospective study was carried out on 49 patients (30 men, 19 women; mean age, 26.7 years) treated for osteosarcoma with HD-MTX. The population and individual pharmacokinetics parameters were computed, before the identification of the relevant covariates. Different LSSs were then tested, to predict accurately when the MTX plasma concentrations would drop below 0.2 micromol/l, the threshold associated with the end of the rescue of leucovorin with alkaline hydration. Two main covariates (creatinemia clearance and alanine aminotransferase) were correlated with MTX clearance. Conversely, the impact of body surface area on MTX pharmacokinetics was weak, suggesting that dosing schedules based on body surface area were inadequate and potentially hazardous. A new LSS predicting accurately when the MTX concentration would reach 0.2 micromol/l has been validated; blood samples are stopped as soon as the MTX concentration drops to 1 micromol/l. With this LSS, our retrospective study suggests that 60% of the patients would have left the hospital earlier than they actually did owing to a better forecasting of the MTX decrease, thus improving their quality of life while improving the cost-effectiveness for the institute. HD-MTX can be administered safely using an adaptive-dosing strategy with drug monitoring. Moreover, pharmacokinetic modeling permits the accurate forecasting of the MTX elimination profile, thus allowing for a better management of the postinfusion care of cancer patients treated with particularly high doses of this drug.

Cisplatin (CDDP) is an anticancer agent widely used in testicular cancer, for which pharmacokinetic (PK)/pharmacodynamic relationships have usually been based upon measurement of its unbound fraction in plasma. Because it has been shown that free CDDP clearance can be related to patient's body surface area (BSA), dosage is mostly adjusted a priori using only this single parameter, with mixed results for accurately predicting CDDP exposure and reducing toxicities. In contrast, the authors present here an original, 5-day continuous infusion schedule, coupled to a daily Bayesian adaptive dosing with feedback strategy, based upon the rapid assay of total, rather than free, CDDP in plasma. Nineteen patients (66 therapeutic courses) were treated with platinum-based combinational therapy. Plasma samples were analyzed to allow real-time Bayesian estimation of individual PK parameters with subsequent prospective dose adjustment in order to reach a target Cmax (Cend) of 1.95 mg/L of total platinum. Performance of the Bayesian dosing method was evaluated by comparing target Cmax with achieved Cmax. The mean+/-SD Cmax achieved was 1.93+/-0.16 mg/L. No statistically significant difference was observed between experimental and target values (P>0.05, t test), and Cend achievement was done with an overall 6.6% precision, a performance to be compared with the initial 54% interpatient variability observed in CDDP clearance. A nonlinear mixed effect model population PK analysis was subsequently performed to identify retrospectively the covariates associated with PK parameters of total CDDP. It showed a good correlation (r=0.84, P=0.004) between total platinum clearance and therapeutic course number. A weaker correlation (r=0.59) was found between BSA and total CDDP clearance and, importantly, no additional relationship was established with BSA when successive therapeutic courses, and not only the first one, were considered. This highlights the critical importance of total drug accumulation on CDDP pharmacokinetics when several infusions are to be administered in a row and, therefore, the need for real-time dose individualization that takes into account the course number, rather than BSA. Finally, doses of CDDP administered during each course were significantly higher (+20%, P<0.01) than the ones classically normalized with BSA, thus leading to an overall greater drug exposure in the patients. It is noteworthy that despite these markedly higher doses, little severe toxicity was reported, and all of the patients presented in this study were still alive and disease free after a follow-up of up to 15 years.

The myelotoxicity of most chemotherapeutic regimens used to treat children and adolescents with cancer require the use of daily subcutaneous administration of hematological growth factors (mainly granulocyte colony-stimulating factor). Recently, pegfilgrastim (Neulasta), a product with a long half-life, resulting in once-per-cycle dosage, was introduced to prevent neutropenia in adults, and provided safety and efficacy similar to that provided by daily injection of filgrastim. To evaluate retrospectively the use of pegfilgrastim in children with cancer, we conducted a single-center retrospective study evaluating the use of pegfilgrastim in patients over 40 kg, who received chemotherapy for cancer from September 2003 to December 2005. A single subcutaneous injection of pegfilgrastim 100 μg/kg (maximum dose 6 mg) per chemotherapy cycle in children receiving myelosuppressive chemotherapy was given. One hundred and twenty-six administrations of pegfilgrastim were analyzed in 28 pediatric patients treated for cancer (11 girls, 17 boys) with a median age of 14.5 years (range 12–18 years) and median weight of 50.5 kg (range 40–82 kg). Patients received a median dose of pegfilgrastim of 100 μg/kg (range 73–117). The median total number of injections per patient was 4 (range 1–14). The incidence of grade 4 neutropenia by cycle was 48%, the mean duration of neutropenia was 3 days (range 1–13 days). The median values of absolute neutrophil count nadir was 0.425×10⁹/l (range 0–9.9×10⁹). Febrile neutropenia occurred in 18 of the 126 patients on pegfilgrastim use (14%) with full recovery in all patients. The median total duration of intravenous antibiotic therapy was 5 days (range 2–14 days). Bone pain (four) and headaches (two) were the most frequent adverse events reported. No correlation was found between the administered dose of Neulasta and hematological data. In conclusion, the use of pegfilgrastim was safe and well tolerated in children with cancer treated with myelosuppressive chemotherapy. Safety and efficacy of pegfilgrastim must be compared with filgrastim and evaluated in younger children with lower body weight.