Methotrexate

Antimetabolite / DMARD

Drug Class: Antimetabolite / DMARD
Mechanism of Action (MOA): Inhibits dihydrofolate reductase → ↓ purine/pyrimidine synthesis (antiproliferative and immunomodulatory).
Black Box Warning: Embryo-fetal toxicity (abortifacient/teratogen), hepatotoxicity, myelosuppression, serious/opportunistic infection, renal toxicity, pulmonary toxicity, severe dermatologic reactions, GI toxicity (diarrhea/stomatitis), tumor lysis syndrome, and lymphoma.
Clinical Notes: RA, psoriasis, ectopic pregnancy, chemotherapy. Dose WEEKLY (not daily) for RA; supplement folic acid; leucovorin rescue. Avoid in pregnancy.
Source: FDA label