Trimethoprim works by blocking the production of tetrahydrofolic acid from dihydrofolic acid in bacteria. It does this by binding to and reversibly inhibiting the enzyme dihydrofolate reductase, which is necessary for bacteria to make nucleic acids and proteins. When combined with sulfamethoxazole, which blocks an earlier step in the same pathway, the two drugs work together to stop bacteria from growing and multiplying.

This dual action makes the combination especially effective against a wide range of bacteria, including those that can cause infections in people with weakened immune systems, such as those with blood cancers. It is particularly important for preventing and treating Pneumocystis jirovecii pneumonia (PJP), a serious lung infection that can affect people with blood cancers or those undergoing chemotherapy.

trimethoprim

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