Patient characteristics associated with high-risk methotrexate concentrations and toxicity.

Abstract

PURPOSE Following high-dose methotrexate (HD-MTX) treatment, delayed MTX elimination is an important problem because it necessitates increased leucovorin rescue and additional hospitalization for hydration and urinary alkalinization. Our purpose was to identify factors associated with high-risk MTX plasma concentrations (defined by plasma concentration > or = 1.0 mumol/L at 42 hours from the start of MTX) and with toxicity. PATIENTS AND METHODS Variables associated with MTX concentrations and toxicity were assessed in 134 children treated with one to five courses of HD-MTX (900 to 3,700 mg/m2 intravenously [i.v.] over 24 hours for a total of 481 courses) for acute lymphoblastic leukemia (ALL). RESULTS High-risk MTX concentrations, toxicity (usually mild mucositis), and delay in resuming continuation chemotherapy occurred in 106 (22%), 123 (26%), and 66 (14%) of 481 courses, respectively. Using a mixed effects model for repeated measures, high-risk MTX concentrations were significantly associated with a higher MTX area-under-the-concentration-time curve (AUC), low urine pH, emesis, low MTX clearance, low urine output relative to intake, use of antiemetics during the MTX infusion, and concurrent intrathecal therapy (all p values < .01). Clinical toxicities and delay in resumption of continuation chemotherapy due to myelosuppression were more common in those with high 42-hour MTX concentrations, despite increased leucovorin rescue for all patients with high-risk MTX concentrations. However, with individualized rescue, no patient developed life-threatening toxicity. A more aggressive hydration and alkalinization regimen for subsequent courses reduced the frequency of high-risk MTX concentrations to 7% of courses (13 of 183) (P = .0001), and the frequency of toxicity decreased to 11% of courses (P = .0074). CONCLUSION This study identified several clinical variables that influence MTX disposition that, when modified, can reduce the frequency of high-risk MTX concentrations and toxicity.