Olsalazine Sodium

Olsalazine sodium is a locally acting gastrointestinal anti-inflammatory agent primarily used in veterinary medicine to treat **chronic colitis** in dogs. It serves as an alternative for patients that are unresponsive to or cannot tolerate **sulfasalazine** (often due to the sulfa moiety causing side effects like keratoconjunctivitis sicca). Structurally, it is a prodrug consisting of two molecules of **5-aminosalicylic acid (5-ASA, mesalamine)** linked by an azo bond. Because it lacks the sulfapyridine moiety found in sulfasalazine, it generally has a lower risk of inducing immune-mediated side effects, though tear production issues can still occasionally occur. *Clinical Pearl:* While olsalazine is more expensive than sulfasalazine, its targeted delivery and lack of a sulfa component make it a valuable second-line therapy for inflammatory bowel disease (IBD) localized to the large intestine.

กลไกการออกฤทธิ์: Olsalazine is a prodrug that passes through the stomach and small intestine largely intact. Upon reaching the colon, **bacterial azoreductase enzymes** (produced by normal colonic flora) cleave the azo bond, releasing two molecules of **5-ASA (mesalamine)**. * **5-ASA** acts locally on the colonic mucosa. * It inhibits the **cyclooxygenase (COX)** and **lipoxygenase (LOX)** pathways → decreasing the production of pro-inflammatory prostaglandins and leukotrienes. * It also acts as a **free radical scavenger**, reducing oxidative tissue damage in the inflamed colon.

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