Directly measured GFR is preferred for initial dosing when eGFR < 60 mL/min/1.73 m2, especially when methotrexate dose ≥ 500 mg/m2 or when eGFR is unreliable (e.g., extremes of body composition, amputees, paraplegia).
Monitor kidney function before, during and after methotrexate administration to identify signs of kidney function deterioration. Monitoring of methotrexate levels is essential as delayed methotrexate excretion is potentially an emergency situation. Methotrexate levels to be monitored every 24 hours until level is less than 0.1 micromol/L.
Methotrexate exits slowly from third space compartments (e.g. pleural effusions or ascites), resulting in a prolonged terminal plasma half-life and unexpected toxicity. In patients with significant third space accumulations, it is advisable to evacuate the fluid before treatment and to monitor plasma methotrexate levels.
Glucarpidase is recommended in patients with high dose methotrexate (HDMTX)-induced acute kidney injury and delayed methotrexate clearance. It can rapidly lower methotrexate levels and early administration within 48 to 60 hours from the start of the HDMTX infusion is critical, as life-threatening toxicities may not be preventable beyond this time point.1
Read more about high dose methotrexate-induced toxicity and methotrexate toxicity in sarcoma.
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