trimethoprim + sulfisoxazole

Trimethoprim + sulfisoxazole is an oral combination antibiotic consisting of the dihydrofolate reductase inhibitor trimethoprim and the sulfonamide antibiotic sulfisoxazole. This fixed-dose combination is primarily used in pediatric patients for the treatment of acute otitis media (middle ear infection) caused by susceptible strains of bacteria. The two components act synergistically to inhibit sequential steps in bacterial folate synthesis, resulting in enhanced antibacterial activity compared to either agent alone. Trimethoprim inhibits bacterial dihydrofolate reductase, blocking reduction of dihydrofolic acid to tetrahydrofolic acid; sulfisoxazole inhibits dihydropteroate synthase, preventing conversion of para-aminobenzoic acid (PABA) into dihydropteroic acid—a precursor to folic acid. This dual blockade disrupts DNA synthesis and leads to bacteriostatic or bactericidal effects depending on concentration and organism.

Brand names

Pediazole

Other names

trimethoprim and sulfisoxazoleTMP-SIZTMP/sulfisoxazole