Consider a directly measured GFR for initial dosing when eGFR < 60mL/min/1.73 m2, especially when eGFR is unreliable (e.g., extremes of body composition, amputees, paraplegia).
Consider monitoring of kidney function before, during and after methotrexate administration to identify signs of kidney function deterioration.
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.
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