Methotrexate monitoring

What it is

Methotrexate is a disease-modifying antirheumatic drug (DMARD) and a purine antimetabolite. In rheumatoid arthritis it is the DMARD given first, with hydroxychloroquine second, and it is taken once weekly rather than every day. The same drug turns up in many other diseases: as a systemic treatment in psoriasis, as the long-term immunosuppressant therapy that follows steroids in polymyositis and dermatomyositis, in low dose with prednisone, on limited evidence, for the skin disease of systemic sclerosis, for maintaining remission in JIA, as CNS prophylaxis in acute lymphoblastic leukemia where it is given intrathecal or systemic, and as single dose medical treatment for ectopic pregnancy. For patients who are intolerant to methotrexate the alternative treatments are leflunomide and sulfasalazine.

The ectopic pregnancy protocol sets out how it works: methotrexate is a folic acid antagonist that inactivates dihydrofolate reductase and the de novo synthesis of purines and pyrimidines, and therefore cellular DNA, so it acts on rapidly dividing trophoblastic cells and prevents their multiplication.