Ulcerative colitis: Timeline to a cure

Figure 3 The reduction of the azo bond in sulfasalazine produces 5-aminosalicylic acid and sulfapyridine. While unconjugated 5-aminosalicylic acid (5-ASA) is predominantly absorbed in the small intestine before it can reach the colon, sulfasalazine largely remains unabsorbed during its transit through the small intestine. Upon reaching the colon, bacterial azo reductases reduce the azo bond, releasing free reduced 5-ASA and sulfapyridine. This reduction reaction introduces an amino group to the No. 5 carbon in the aromatic ring of salicylic acid, resulting in the formation of reduced 5-ASA. Reduction of the azo bond enhances the electron density of the resulting 5-ASA, enabling it to function as a reducing agent and effectively neutralize hydrogen peroxide in the colonic lumen. 5-ASA: 5-aminosalicylic acid.