Some sulfon-amide derivatives, such as sulfaguanidine, are so insoluble that they are not absorbed from the Gl tract (<5%).

Phthalylsulfathiazole and succinylsulfathiazole undergo bacterial hydrolysis in the lower Gl tract with the consequent release of active sulfathiazole.

Salicylazosulfapyridine (sulfasalazine) is also hydrolyzed in the large intestine to sulfapyridine and 5-aminosalicylic acid, an anti-inflammatory agent that might be used for the management of ulcerative colitis in dogs.