Fig. 11: Pathway for the Synthesis of Tetrahydrofolic Acid, a Cofactor
Needed for the Synthesis of DNA and RNA Nucleotides

Sulfonamides such as sulfamethoxazole tie up the enzyme pteridine synthetase while trimethoprim ties up the enzyme dihydrofolic acid reductase. As a result, tetrhydrofolic acid is not produced by the bacterium. (Purines = adenine, guanine)

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