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C₂₀H₂₂N₈O₅

http://www.rxlist.com/cgi/generic/mtx.htm

Seeger et al.; J.Amer.Chem.Soc.; 71; 1753,1757(1949)

454.44 g/mol

195 ^oC

2600 mg/L

Solid

-1.08

Liquid; Powder for solution; Solution; Tablet (oral, in 5 mg, 7.5 mg, or 10 mg)

For the treatment of gestational choriocarcinoma, chorioadenoma destruens and hydatidiform mole. Also for the treatment of severe psoriasis and severe, active, classical or definite rheumatoid arthritis.

Methotrexate is an antineoplastic anti-metabolite. Anti-metabolites masquerade as purine or pyrimidine - which become the building blocks of DNA. They prevent these substances becoming incorporated in to DNA during the "S" phase (of the cell cycle), stopping normal development and division. Methotrexate inhibits folic acid reductase which is responsible for the conversion of folic acid to tetrahydrofolic acid. At two stages in the biosynthesis of purines and at one stage in the synthesis of pyrimidines, one-carbon transfer reactions occur which require specific coenzymes synthesized in the cell from tetrahydrofolic acid. Tetrahydrofolic acid itself is synthesized in the cell from folic acid with the help of an enzyme, folic acid reductase. Methotrexate looks a lot like folic acid to the enzyme, so it binds to it quite strongly and inhibits the enzyme. Thus, DNA synthesis cannot proceed because the coenzymes needed for one-carbon transfer reactions are not produced from tetrahydrofolic acid because there is no tetrahydrofolic acid. Methotrexate selectively affects the most rapidly dividing cells (neoplastic and psoriatic cells). Methotrexate is also indicated in the management of severe, active, classical, or definite rheumatoid arthritis.

Generally well absorbed with a mean bioavailability of about 60%.

Symptoms of overdose include bone marrow suppression and gastrointestinal toxicity. LD₅₀=43mg/kg(orally in rat).

Patients should be informed of the early signs and symptoms of toxicity, of the need to see their physician promptly if they occur, and the need for close follow-up, including periodic laboratory tests to monitor toxicity. 

Both the physician and pharmacist should emphasize to the patient that the recommended dose is taken weekly in rheumatoid arthritis and psoriasis, and that mistaken daily use of the recommended dose has led to fatal toxicity. Patients should be encouraged to read the Patient Instructions sheet within the Dose Pack. Prescriptions should not be written or refilled on a PRN basis. 

Patients should be informed of the potential benefit and risk in the use of methotrexate. The risk of effects on reproduction should be discussed with both male and female patients taking methotrexate. 

Humans and other mammals