Known brand names include Trexall.
A pill, usually taken once a week, for rheumatoid arthritis, severe psoriasis, and juvenile arthritis, and part of chemotherapy for some blood cancers. It blocks an enzyme cells need to use folate, and taking a weekly dose every day by mistake has caused deaths.
Methotrexate blocks dihydrofolate reductase, an enzyme cells need to turn folate into the active form they use to make the building blocks of DNA. Without that active folate, cells have trouble copying and repairing their DNA, so they cannot divide normally. Cells that divide quickly are hit hardest, such as cancer cells, bone marrow, the lining of the mouth and gut, and the cells of an unborn baby. How it helps rheumatoid arthritis and psoriasis is not known, though it may calm the immune system and slow the growth of skin cells.
Taken by mouth, it reaches its highest level in the blood within 6 hours, food slows that uptake, and the kidneys remove most of it. For arthritis, most people who improve do so within 3 to 6 weeks, though some take up to 12 weeks. Because it acts on all fast-dividing cells, it can cause mouth sores, low blood counts that lead to infection or bleeding, and harm to an unborn baby. Weak kidneys or fluid pooled around the lungs or in the belly slow its removal, which raises the risk of serious side effects.
Methotrexate tablets treat rheumatoid arthritis, a disease in which the immune system attacks the joints and causes pain, swelling, and loss of function. It also treats severe psoriasis, a skin disease with red, scaly patches, and polyarticular juvenile idiopathic arthritis, a childhood arthritis that affects many joints. In cancer care, it is part of combination treatment for acute lymphoblastic leukemia, a cancer of the white blood cells, and for certain lymphomas, including mycosis fungoides, a lymphoma that first shows up in the skin. The aim is to slow the growth of cancer cells, clear the scaly skin patches, and calm arthritis.
Adults take it for rheumatoid arthritis, severe psoriasis, and the lymphomas, children take it for juvenile arthritis, and both take it for the leukemia. It is a tablet swallowed at home, often once a week, and people using it for arthritis or psoriasis are also given folic acid, a vitamin, to lower the risk of side effects. In children, it has been shown to work and be safe only for the leukemia and juvenile arthritis. It is not given to people who cannot swallow a tablet, and it must not be used in pregnancy to treat arthritis or psoriasis.
Mouth sores, nausea, stomach upset, and abnormal liver tests are the most common effects, along with tiredness, dizziness, hair loss, and skin that burns easily in the sun. The label treats low blood counts, serious infections, liver scarring, lung inflammation, kidney damage, severe skin reactions, nerve and brain problems, and bleeding or holes in the bowel as serious, and some of these can be fatal. It can cause birth defects or the loss of a pregnancy, and taking a once-weekly dose every day by mistake has caused deaths.
A clinician may order these while someone is taking it.
This is the boxed warning, the warning the FDA label prints first.
Embryo-fetal toxicity, hypersensitivity, severe adverse reactions, and medication errors. It can cause fetal death and is contraindicated in pregnancy for non-neoplastic diseases; patients treated for cancer need effective contraception. It is contraindicated after severe hypersensitivity, including anaphylaxis. Serious and fatal toxicity of the marrow, GI tract, liver, lungs, skin, and kidneys calls for close monitoring and withholding or stopping as appropriate. Taking it once daily by mistake has caused deaths.
Sources: [1]