Review article: new developments in the use of 5-aminosalicylic acid in patients with inflammatory bowel disease.

Sulphasalazine is composed of sulphapyridine and mesalazine (5-aminosalicylic acid, 5-ASA or mesalazine) joined by an azo bond. Sulphasalazine has been used clinically for 40 years but less than 10 years ago it was recognized that the active moiety is 5-ASA. Sulphapyridine appears to act only as a carrier molecule to deliver mesalazine to the bowel, yet it is the sulphapyridine which appears to be responsible for many of the adverse effects observed with sulphasalazine. Normally, mesalazine is rapidly absorbed from the upper gastrointestinal tract. Since the action of mesalazine is thought to be locally at the site of disease in the intestine, the 5-ASA must be 'protected' to ensure its release in the terminal ileum and colon, the site of bowel inflammation in patients with Crohn's disease or ulcerative colitis. Recent clinical studies have confirmed the efficacy of topical (suppositories and enemas) therapy for ulcerative proctitis and left-sided colitis; oral mesalazine has been proven to be useful for the treatment of acute ulcerative colitis and for the maintenance of remission. There is preliminary evidence for the clinical usefulness of mesalazine in acute Crohn's disease as well as for the maintenance of remission.