Synonyms: Sulfamethoxazole Imp. B (EP), Sulfamethoxazole USP Related Compound B, Sulfamethoxazole USP RC B, 4-[[(4-Aminophenyl)sulphonyl]amino]-N-(5-methylisoxazol-3-yl)benzenesulphonamide, Sulfamethoxazole Related Compound B, Sulfamethoxazole Impurity B