Methotrexate interferes with cell growth

Methotrexate may be given as a pill or as a shot in the vein (intravenously, or iv) or in the muscle (intramuscularly, or im). By blocking the enzyme dihydrofolate reductase, methotrexate inhibits the production of thymidine, a requirement for dna synthesis. Methotrexate interferes with cell growth and specifically interferes with rapidly dividing cells. Conditions that produce rapid cell division include neoplastic disease, autoimmune diseases (rheumatoid arthritis), and pregnancy.