Delayed excretion of high-dose methotrexate in pediatric acute leukemia correlates with laxative and constipation management.

Background: Delayed excretion of high-dose methotrexate (HD-MTX) in pediatric acute lymphoblastic leukemia (ALL) can result in significant morbidity. While methotrexate is primarily renally excreted, HD-MTX may overwhelm renal excretion and increase reliance on fecal elimination. This study evaluated the association between laxative use for constipation and delayed excretion of HD-MTX.

Methods: This multisite chart review included pediatric patients with ALL (2010-2020) who received HD-MTX (5 g/m²). Delayed excretion was defined as a serum MTX concentration greater than 0.4 µM at Hour 48. We identified use of laxative medications after each HD-MTX infusion, with receipt of two or more doses considered a proxy for constipation. Multilevel logistic regression models evaluated associations between clinical factors and delayed HD-MTX excretion to account for multiple MTX cycles per individual.

Results: A total of 533 eligible patients received 1875 HD-MTX infusions. Patients were mostly male (59.8%), Hispanic (56.7%), with a median age of 9.5 years. Delayed excretion was observed following 42.7% of HD-MTX infusions, and patients received two or more laxative doses during 19.9% of infusions. Independent of other factors, individuals who received two or more laxative doses were nearly 60% (odds ratio 1.58; 95% confidence interval: 1.19-2.09; p = .002) more likely to experience delayed excretion compared to those receiving fewer than two laxative doses.

Conclusion: Receipt of at least two laxative doses was independently associated with delayed methotrexate excretion in pediatric patients with ALL. Future prospective studies are needed to confirm the secondary effects of constipation and confirm the association with constipation and identify clinical benefits that optimize drug excretion.