Trimethoprim, a diaminopyrimidine compound, is a dihydrofolate reductase inhibitor. It is frequently used as a single agent for the treatment of uncomplicated urinary tract infections. It can be combined with sulfamethoxazole (as co-trimoxazole) for antimicrobial synergy. This combination is effective against a variety of gram-negative and gram-positive bacteria (including methicillin-resistant Staphylococcus aureus), some protozoa, and as prophylaxis against Pneumocystis jirovecii.
