During a chemotherapy treatment, a patient inadvertently received a 10 fold dosing error of IV methotrexate. Glucarpidase was given shortly after the dosing error was identified. 48 hours later, the serum methotrexate concentration was still markedly elevated. What is the likely culprit?
False elevation of serum methotrexate levels due to cross-reactivity of DAMPA with immunoassay tests. DAMPA cross reacts with methotrexate in standard methotrexate immunoassay tests. This cross reactivity falsely elevates methotrexate levels for 48 hours though in a recent case report, this false elevation persisted for nearly 96 hours. HPLC testing is a more accurate reflection of methotrexate levels regardless of glucarpidase administration.
Gulley SL. et al. Monitoring Methotrexate Levels in a Patient After Glucarpidase Administration: A Case Report. J Hematol Oncol Pharm. 2020;10(3):154-157