Methotrexate (MTX, amethopterin) is a folate antimetabolite. It is an analog of aminopterin, which is also derived from folic acid. The molecular structure of methotrexate differs from folic acid in that it has a hydroxyl
group in place of the 4-amino group on the pteridine ring and there is no methyl group at the N position.
Methotrexate is an antineoplastic drug used solely or in combination with other antineoplastic drugs for the treatment of leukemia and other diseases. Relatively low doses of methotrexate have been used in the treatment of nonmalignant diseases such as severe psoriasis, asthma, rheumatoid arthritis, sarcoidosis, and transplantation therapy.
Intermediate to high doses of methotrexate with Leucovorin rescue have been used with favorable results in the treatment of osteogenic sarcoma, leukemia, non-Hodgkin’s lymphoma, lung and breast cancer. Methotrexate levels are monitored to avoid excessive toxic effects of the drug and to determine when to intervene with counter-acting ‘rescue’ therapy. Adverse reactions include myelosuppression, stomatitis, nausea,
vomiting, convulsions, liver and renal abnormalities, anemia, leukopenia, thrombocytopenia, osteoporosis, neurotoxicity, and leukoencephalopathy.
There are no current indications for monitoring low dose methotrexate therapies.