23.4 : 用于治疗炎症性肠病（IBD）中溃疡性结肠炎的药物

Ulcerative colitis is characterized by mucosal inflammation of the colon.

The first-line agent, 5-aminosalicylic acid or 5-ASA, inhibits leukotriene and prostaglandin synthesis, scavenges free radicals, and suppresses various immune cell activities. It may also block nuclear factor-κB, reducing proinflammatory cytokine production.

5-ASA is available in various formulations to counter its high small intestine absorption.

In azo prodrugs like sulfasalazine and balsalazide, active 5-ASA forms an azo bond with an inert compound, while in olsalazine, it exists as a dimer. Upon reaching the colon, the azo bond is cleaved by colonic bacteria, increasing 5-ASA levels in affected colon areas.

Common side effects include headache, nausea, fatigue, rarely hemolytic anemia, and hepatitis.

Coated mesalamine formulations, enclose 5-ASA molecules within a pH-sensitive enteric coat or semipermeable ethylcellulose film to limit GI absorption at the proximal end, ensuring increased drug delivery to the colon.

Mesalamine's adverse effects include headache, dyspepsia, skin rash, and rarely interstitial nephritis.