A pharmacologically-based approach to high dose methotrexate administration to investigate nephrotoxicity and acute kidney injury biomarkers in children and adolescents with newly diagnosed osteosarcoma.

PURPOSE High dose methotrexate (HDMTX) acute kidney injury (AKI) results in prolonged hospitalization and treatment delays. Using a pharmacologically-based approach, HDMTX was administered with standard combination therapy to patients with osteosarcoma; nephrotoxicity was assessed. METHODS Patients were randomized by cycle to 4 h or 12 h HDMTX (12 g/m2) infusions administered with hydration, alkalization and leucovorin rescue. Urinalysis, AKI biomarkers, and estimated glomerular filtration rate using serum creatinine or cystatin C (GFRCr or GFRcysC) were obtained. Serum and urine methotrexate concentrations [MTX] were measured. RESULTS Patients (n = 12), median (range) age 12.4 (5.7-19.2) years were enrolled; 73 MTX infusions were analyzed. Median (95% Confidence Interval) serum and urine [MTX] were 1309 (1190, 1400) µM and 16.4 (14.7, 19.4) mM at the end of 4 h infusion and 557 (493, 586) µM and 11.1 (9.9, 21.1) mM at the end of 12 h infusion. Time to serum [MTX]   95%. CONCLUSIONS Reducing peak serum and urine MTX concentration by prolonging the infusion duration did not alter risk of acute kidney injury. GFRcysC was decreased at the end of therapy. Proteinuria and elevations in AKI biomarkers indicate that direct tubular damage contributes to HDMTX nephrotoxicity. CLINICAL TRIAL NCT01848457.