trimethoprim-sulfamethoxazole

Trimethoprim-sulfamethoxazole is a synthetic fixed-dose antibacterial combination marketed under brands such as Bactrim/Septra in U.S. practice. It works by blocking sequential steps in bacterial folate synthesis and is used across multiple susceptible bacterial infections including urinary tract, otitis media, bronchitis exacerbations, shigellosis, Pneumocystis pneumonia treatment/prophylaxis, and travelers' diarrhea.

Drug Class

Synthetic antibacterial combination (sulfonamide + dihydrofolate reductase inhibitor)

Approval Status

FDA approved (multiple legacy and generic labels active; this cited FDA label revision is 2021)

Mechanism of Action

Sulfamethoxazole competitively inhibits dihydropteroate synthase while trimethoprim reversibly inhibits dihydrofolate reductase, producing sequential blockade of folate-dependent nucleic acid/protein synthesis.