RESUMEN
High-dose methotrexate is included in chemotherapy regimens used to treat a number of malignant neoplasms. Methotrexate plasma concentration is considered the best toxicity predictor. Monitoring methotrexate plasma concentrations is standard practice in the identification of at-risk patients, the titration of folinic acid doses, and the establishment of corrective measures. Methotrexate is a kidney-cleared weak acid, and renal function impairment may retard methotrexate clearance. A case of severe methotrexate-induced toxicity secondary to renal failure is reported in a patient with non-Hodgkin s lymphoma receiving methotrexate at a dose of 1 g/m2. Corrective measures included folinic acid rescue therapy, cholestyramine resin administration, hydration and urine alkalinization, urine pH monitoring, and extracorporeal clearance techniques.