Methotrexate: uses, mechanism, monitoring, and safety

How it works

The drug interferes with folate metabolism by inhibiting the enzyme dihydrofolate reductase, which reduces the availability of nucleotides needed for DNA and RNA synthesis. This mechanism explains both its anti‑proliferative action against cancer cells and its immunomodulatory effects in autoimmune disease. Many regimens combine methotrexate with folic acid supplementation to reduce side effects while preserving benefit.

Primary uses

• Cancer therapy: used in some leukemias, lymphomas and solid tumours as part of chemotherapy protocols — often at higher, intermittent doses; see cancer treatment.
• Autoimmune and inflammatory diseases: a cornerstone treatment for rheumatoid arthritis, psoriasis and some inflammatory bowel conditions, where it acts as a disease‑modifying antirheumatic drug; see autoimmune conditions.
• Reproductive care: used, in specific clinical circumstances, to manage early ectopic pregnancy or as part of a regimen for medical termination of pregnancy; see medical abortion and pregnancy.
• Specialized administration: in oncology it can be given orally, subcutaneously, intravenously or intrathecally depending on the indication.

Safety, monitoring and notable considerations

Methotrexate can cause bone marrow suppression, liver toxicity, lung inflammation, stomatitis and gastrointestinal symptoms. It is teratogenic and contraindicated in pregnancy; for detailed medication information consult drug information. Routine monitoring typically includes blood counts, liver enzymes and renal function because impaired kidney clearance increases toxicity risk.

Interactions and precautions include caution with nonsteroidal anti‑inflammatory drugs, alcohol and other agents that affect renal function or hepatic metabolism. Low‑dose regimens commonly include folic acid to reduce adverse effects without eliminating therapeutic benefit.

History and significance

Derived from work on folate analogues in the mid‑20th century, methotrexate transformed treatments for some cancers and later became a mainstay therapy for inflammatory disease. Its wide application and narrow therapeutic index make it one of the best‑known examples of a drug whose dose, indication and monitoring determine both safety and effectiveness.