Sulfamethoxazole inhibits bacterial synthesis of dihydrofolate by competing with p-aminobenzoic acid. Sulfamethoxazole tablets inhibit the production of tetrahydrofolate from dihydrofolate by binding to the essential enzyme dihydrofolate reductase and vice versa. This medicine is a combination of two antibiotics sulfamethoxazole and trimethoprim. It is used to treat a variety of bacterial infections.