Methotrexate is an antimetabolite anticancer and immunosuppressive drug.
It works by inhibiting dihydrofolate reductase, which interferes with DNA synthesis and cell replication—particularly affecting rapidly dividing cells.
It can be administered intravenously (IV), intramuscularly (IM), intra-arterially, or intrathecally (route depends on indication).

Cancer (Oncology)

• Acute lymphoblastic leukemia (ALL)

• Non-Hodgkin’s lymphoma

• Breast cancer

• Osteosarcoma (high-dose regimens)

• Choriocarcinoma & gestational trophoblastic disease

• Head & neck cancers

• Lung cancer (in combination therapy)

Common Side Effects

• Nausea, vomiting

• Mouth ulcers (stomatitis)

• Loss of appetite

• Fatigue

• Hair thinning

• Injection-site reactions

Serious Side Effects

• Bone marrow suppression

  • Low WBCs (infection risk)

  • Low platelets (bleeding)

  • Anemia

• Liver toxicity (raised liver enzymes, fibrosis with long use)

• Kidney toxicity (especially high doses)

• Lung toxicity (methotrexate pneumonitis)

• Severe skin reactions

• Neurotoxicity (with intrathecal use)

Dosage varies widely and must be determined by a specialist.

Cancer Therapy 

• Low dose:

  • 20–40 mg/m² IV or IM once weekly (combination regimens)

• High dose (e.g., osteosarcoma):

  • 1–12 g/m² IV, followed by leucovorin rescue

Rheumatoid Arthritis / Psoriasis

• 7.5–25 mg once weekly (IM or SC/PO equivalent)

Never give methotrexate daily for RA/psoriasis — risk of fatal toxicity