METHOTREXATE
It has a cell cycle specific action-kills cells in S phase; primarily inhibits DNA synthesis, but also affects RNA and protein synthesis. It blocks the convesion of a essential coenzyme required for one carbon transfer reaction in de novo purine synthesis and amino acid inter conversions.Lymphoblastic leukaemia. Choriocar-cinoma.
Lymphoblastic leukaemia: 20-40 mg/sqm. body surface area twice weekly i.v or i.m. Maint dose: 15-30 mg/sqm 1-2 times weekly. Chorio carcinoma: 15-30 mg daily for 5 days.
Severe leucopenia or thrombocytopenia. Serious anaemia
Use of folinic acid rescue has permitted much higher doses of methotrexate. Hepaticand renal dysfunction. C.N.S. disturbance. Bone marrow depression. Paediatrics: Use only in cancer treatment. Pregnancy: Contraindicated due to its teratogenic effects. Lactation: Should not be used. Elderly: Use with caution.
Megaloblastic anaemia, pancytopenia, Desquamation and bleeding may occur in G.I.T.
Salicylates, sulphonamides, phenytoin, henylbutazone, tetracyclines, chloramphenicol and para-aminobenzoic acid increase toxicity. Asparginase reduces toxicity.
