METHOTREXATE

Methotrexate (rINN) abbreviated MTX and formerly known as amethopterin, is an antimetabolite and antifolate drug used in treatment of cancer, autoimmune diseases and as an abortifacient in the induction of medical abortions. It acts by inhibiting the metabolism of folic acid. Methotrexate competitively inhibits dihydrofolate reductase (DHFR), an enzyme that participates in the tetrahydrofolate synthesis. The affinity of methotrexate for DHFR is about one thousand-fold that of folate for DHFR. Methotrexate acts specifically during DNA and RNA synthesis, and thus it is cytotoxic during the S-phase of the cell cycle. Logically, it therefore has a greater toxic effect on rapidly dividing cells which replicate their DNA more frequently, and thus inhibits the growth and proliferation of these non-cancerous cells. Lower doses of methotrexate have been shown to be very effective for the management of rheumatoid arthritis, Crohn's disease, and psoriasis.