Name: Methotrexate (Rheumatrex)
Class: Slow-Acting Antirheumatic Agent (AntiMetabolismolite)
Mechanism: Inhib. dihydrofolate reductase ® inhib. of formation of tetrahydrofolic acid ® ¯ synth of purines, thymidylic acid, methionine, and serine ®
¯ DNA/RNA/protein synth. ® eventual cell death.
Absorption: Oral, IV, IM, IT.
Dist.: No CNS unless administered IT.
Metabolism.: Excretion, t½:
Toxicity/S.E.s: Stomatitis, myelosuppression, erythema, rash, urticaria, alopecia, n/v/d. Long term use may ® hepatic fibrosis. High doses may ® crystalluria. Patient must be well hydrated and have alkaline urine to avoid renal toxicity. Also pulmonary toxicity in children. IT admin. ® subacute meningeal irritation, stiff neck, headache, fever; rarely seizures, encephalopathy, paraplegia. C/i w/pregnancy (teratogenic).
Utility: Low doses useful in treating rheumatoid arthritis and severe psoriasis. Effective against acute lymphocytic leukemia, choriocarcinoma, Burkitt’s lymphoma, breast cancer, head/neck carcinomas. High doses are curative for osteogenic sarcoma and choriocarcinoma.