Sulfonamide chemical structure and metabolism. a: Sulfonamide core structure. It is present as sulfonyl-arylamine, where a sufonamide is attached to a benzene ring with an unsubstituted amine (-NH2) moiety at the N4 position. Many other drugs may also contain a sulfonamide (example: furosemide). b: SMX is metabolized intra-hepatically to SMX-NHOH, which is further oxidised to SMX-NO; the later binds covalently to cystein in proteins.