This acts as an antimetabolite of folic acid. It has also immunosuppressant properties.

Indications: maintenance therapy for childhood acute lymphoblastic leukaemia, choricocarcinoma, non- Hodgkin's lymphomas, a number of solid tumours; intrathecal methotrexate is used in the CNS prophylaxis of childhood acute lymphoblastic leukemia, and as a therapy for established meningeal carcinoma or lymphoma.

Cautions: Should be avoided in the presence of significant pleural effusion or ascites because it can accumulate in these fluids, and its subsequent return to the circulation may cause myelosuppression.

Contra-indications: Patients with significant renal and hepatic dysfunction.

Side Effects: bone-marrow suppression (dose-related), gastro-intestinal disturbances (anorexia, nausea, vomiting, and diarrhoea); oral ulceration, stomatitis, pharyngitis; glossitis; gingivitis; hepatotoxicity; interstitial pulmonary fibrosis.

Dose: According to individual protocols. Conventional 15 – 20mg/m2 orally twice weekly or 30-50mg/m2 orally/IV weekly or 15mg/day for 5 days orally/IM every 2-3 weeks.