Individualization of high-dose methotrexate (MTX) dosing is important to achieve therapeutic levels (700-1,000 μM) for osteosarcoma. Therefore we developed a pharmacokinetically (PK) individualized dosage regimen to maintain MTX concentrations of 700 μM (1 h bolus followed by 5 h maintenance infusion) and evaluated its safety and efficacy. Loading and maintenance doses were calculated by the PK parameters based on 2-compartment model analysis. Thirty-two courses of chemotherapy were performed in 9 patients with osteosarcoma. The maximum concentrations during maintenance infusion in 31 courses (97%) were above 700 μM. Only 1 patient developed severe hepatotoxicity as adverse effect. Total body clearance of MTX decreased in 4 patients when weekly MTX chemotherapy was performed for 3 consecutive weeks. Although the clearance was changed, the average MTX concentrations were maintained at about 700 μM by the PK individualization. The 5-year survival rate was 77.8% (7 of 9 patients), and all of them have survived for more than 9 years. This PK individualization is safe and useful for tailoring high-dose MTX therapy to achieve therapeutic levels.
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