Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1073 page)

METHOTREXATE
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   Definition

   Folic acid antagonist. Other names: Folex, Mexate, Trexall.

   
Normal range:
TDM generally performed to ensure plasma/serum concentration <1 μmol/L at 48 hours postinfusion and <0.1 μmol/L at 72 hours postdose

   Use

   Methotrexate is an antineoplastic drug used solely or in combination with other antineoplastic drugs for the treatment of leukemia and other diseases.

   Severe psoriasis, sarcoidosis, and granulomatosis have been treated with methotrexate in relatively low doses.

   High-dose methotrexate (greater than approximately 20 mg/kg body weight) with citrovorum factor rescue have been used with favorable results in the treatment of osteogenic sarcoma, leukemia, non-Hodgkin lymphoma, lung cancer, carcinoma of the head and neck, and breast cancer.

   The efficacy of methotrexate in the treatment of other tumors such as prostate cancer is being investigated.

   Interpretation

   Potential toxicity: Reported therapeutic and toxic ranges are dependent on dose and the time the sample is drawn postdose. Consult protocol to assess toxicity.

   24 hours: >10 μmol/L

   48 hours: >1.0 μmol/L

   72 hours: >0.1 μmol/L