Folic acid antagonist (antimetabolite) → purine nucleotide and thereby ↓ DNA synthesis

Clinical use:- Treatment of severe psoriasis and rheumatoid arthritis- In neoplastic diseases like gestational choriocarcinoma, chorioadenoma, and hydatidiform mole

Side effects:- Pancytopenia and/or macrocytic anemia- Mucositis (particularly stomatitis, enteritis), susceptibility to infection- Hepatotoxicity, nephrotoxicity- Nausea and vomiting, diarrhea- Pulmonary fibrosis and toxicity- Hair loss