INFO - Metabolism of injectable methotrexate

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Last reviewd Jun 2008

" Methotrexate Injection "

Excerpt:

Metabolism

After absorption, methotrexate undergoes hepatic and intracellular

metabolism to polyglutamated forms which can be converted back to

methotrexate by hydrolase enzymes. These polyglutamates act as

inhibitors of dihydrofolate reductase and thymidylate synthetase.

Small amounts of methotrexate polyglutamates may remain in tissues for

extended periods. The retention and prolonged drug action of these

active metabolites vary among different cells, tissues and tumors. A

small amount of metabolism to 7-hydroxymethotrexate may occur at doses

commonly prescribed. Accumulation of this metabolite may become

significant at the high doses used in osteogenic sarcoma. The aqueous

solubility of 7-hydroxymethotrexate is 3 to 5 fold lower than the

parent compound. Methotrexate is partially metabolized by intestinal

flora after oral administration.

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