Sulfametoxydiazine (INN) or sulfamethoxydiazine (USAN: sulfameter) is a long-acting sulfonamide antibacterial, shows bacteriostatic effects against Gram positive and Gram negative bacteria in vivo. It is used as a leprostatic agent and in the treatment of urinary tract infections. Orally active. Sulfonamides block the synthesis of dihydrofolic acid by inhibiting the enzyme dihydropteroate synthase. Sulfonamides are competitive inhibitors of bacterial para-aminobenzoic acid (PABA), which is required for bacterial synthesis of folic acid. Sulfameter is a dihydrofolate reductase (DHFR) inhibitor. Mode of resistance is via the alteration of dihydropteroate synthase or alternative pathway for folic acid synthesis.