[Preliminary evaluation of individualized use of large doses of methotrexate for treatment of osteosarcoma in children and adolescents].

To improve the final treatment results in children with osteosarcoma, we applied after French DD-11 protocol HD MTX increasing with the younger age of patients, modified next on the basis of maximal serum drug concentrations (Cmax) as feed-back dosing. Toxic side effects were analysed according to WHO grading correlated with MTX elimination. We administered 39 HD MTX courses in 13 patients with osteosarcoma: aged 7-20 yrs (median 12 yrs). We performed 301 measurements of MTX concentration using the method of fluorescence polarisation. Therapeutic Cmax of 1000 microM/L and higher were obtained in 20 courses, the mean of lower values was 770 microM/L. We modified the next MTX doses in 23.7% of courses. Drug elimination was good in the majority of cases: in 34 of 39 courses at 24 hrs, in 36 of 39 at 48 hrs. Nevertheless, III and IV degree toxic side-effects accompanied about half of the courses and could not be predicted by MTX serum level measurements. HD MTX therapy with monitoring MTX serum levels proved feasible with acceptable toxicity. Therapeutic MTX levels were obtained in about 60% of cycles in patients with a favourable course of the disease in comparison with 25% in patients with an unfavorable course but the beneficial effect of age-tailored MTX and feed-back dosing on the treatment results will be possible to assess in the next 3 years.