Methotrexate (MTX) is an antineoplastic and immunosuppressive drug effective against malignancies with rapid cell proliferation such as acute lymphoblastic leukemia and certain carcinomas. It can safely be administered over a wide dose range as chemotherapy and also for the treatment of several nononcologic diseases as rheumatoid arthritis or psoriasis. Moderate to high doses of methotrexate can be favorably administered with leucovorin rescue by closely monitoring MTX serum levels to prevent potentially toxic effects. Accurate measurement of MTX levels at ≤ 0.5 µmol/L, therefore, enables determination of nontoxic status.
Methotrexate value should be used in conjunction with information available from clinical evaluation and other diagnostic procedures. Use the same method consistently for individual patient care due to the potential for method-to-method variability.