Validation of the MTXPK Tool in Predicting Glucarpidase Utilization Among Patients With Delayed Methotrexate Clearance: A Retrospective Study.

Introduction Glucarpidase, a recombinant bacterial enzyme, can treat patients with methotrexate (MTX) toxicity. Identifying appropriate administration of glucarpidase can be challenging. MTXPK.org, a web-based clinical decision tool, maps projected MTX clearance for individual patients based on demographics and serum MTX levels to identify patients at the highest risk for toxicity who might benefit from glucarpidase administration. Here, we report our single institution experience with the predictive value of the MTXPK web tool in guiding glucarpidase administration. Methods Retrospective data collection conducted from 2000 through 2023 of patients admitted for high-dose methotrexate (HDMTX) who received glucarpidase therapy. Data required for utilization of the MTXPK tool were collected (age, sex, race, height, weight, MTX dose, creatinine, serum MTX, albumin, and the presence of pleural effusion). Data was input into the MTXPK tool to plot a curve of MTX clearance rate for each patient compared to the population predicted curve. Patient MTX clearance rates that fell below the predicted population rates were candidates for glucarpidase. Results Thirteen patients were included for review, with ages ranging from four months to 72 years, with an average of 47.7 years. Nine patients (69%) were male, and four (31%) were female. Twelve were Caucasian patients (92.3%), and one was a Black patient (7.7%). Average height and weight were 66.6 inches and 83.6 kg, respectively, with an average body surface area (BSA) of 1.99 kg/m. Six patients (46.2%) had lymphoma, two (15.4%) had sarcoma, and five (38.5%) had leukemia. One hundred percent of MTXPK predictions matched published glucarpidase administration guidelines. MTXPK predicted that only eight patients (61.5%) should have received glucarpidase, indicating five (38.5%) of patients were administered the drug unnecessarily. Conclusion Clinicians should utilize MTXPK as an objective tool to assist in clinical decision-making in patients with delayed MTX clearance with the goal of limiting unnecessary use of glucarpidase and avoiding unintended outcomes of MTX toxicity.