RESUMO
<p><b>BACKGROUND</b>High-dose methotrexate (HD-MTX) with folinic acid (leucovorin) rescue is "gold standard" therapy for osteosarcoma. Plasma concentrations of methotrexate (MTX) are closely related to its efficacy and toxicity. Delayed excretion of MTX can lead to serious adverse reactions that may result in treatment cessation, irreversible organ damage, and death. This study focused on the incidence of delayed excretion of MTX in Chinese osteosarcoma patients.</p><p><b>METHODS</b>A total of 1277 osteosarcoma patients were treated with HD-MTX chemotherapy (4291 cycles) from 2010 to 2015. Factors that could influence delayed excretion of MTX (gender, age, number of chemotherapy cycles, and serum concentration of MTX) were analyzed.</p><p><b>RESULTS</b>The incidence of delayed excretion of MTX (serum concentrations at 24 h [C24 h] >5 μmol/L) and severe delayed excretion of MTX (C24 h >20 μmol/L) were 6.19% and 0.86% per patient, and 2.31% and 0.26% per cycle of treatment, respectively. The incidence of severe delayed excretion of MTX was associated with gender, age, and C24 h.</p><p><b>CONCLUSIONS</b>Precaution of delayed excretion of MTX is needed during osteosarcoma treatment using HD-MTX. An optimal individualized rescue strategy can be created with consideration of gender, age, and C24 h.</p>