Trimethoprim belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors. It is an antibiotic used to treat various bacterial infections such as urinary tract infections, traveler's diarrhea, respiratory and middle ear infections.

It works by interfering with the production of tetrahydrofolic acid, a chemical that is necessary in order for bacteria and human cells to produce proteins. Trimethoprim inhibits production of tetrahydrofolic acid by inhibiting the enzyme responsible for making tetrahydrofolic acid from dihydrofolic acid. Trimethoprim inhibits the bacterial enzyme more than the corresponding human enzyme. Therefore, trimethoprim has less effect on the production of tetrahydrofolic acid by humans.

This antibiotic treats only bacterial infections. It will not work for viral infections (e.g., common cold, flu). Unnecessary use or overuse of any antibiotic can lead to its decreased effectiveness.

 

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