Sulfamethoxypyridazine is a sulfonamide consisting of pyridazine having a methoxy substituent at the 6-position and a 4-aminobenzenesulfonamido group at the 3-position. It has a role as an antiinfective agent, an EC 2.5.1.15 (dihydropteroate synthase) inhibitor and a drug allergen. It is a member of pyridazines, a sulfonamide and a sulfonamide antibiotic. It derives from a sulfanilamide.