Regardless of the mode of action, 5-ASA appears to be only effective topically. Rectal administration, therefore, allows for direct targeting of free 5-ASA to the sites of inflammation along the mucosal lumen of the rectum, sigmoid and distal large bowel. In contrast, oral administration of free 5-ASA leads to high systemic absorption with little chance of topical effectiveness in the distal bowel. Following rectal administration, both free and acetylated forms can be found in plasma within 1 to 2 hours post administration. Plasma levels are therefore negligible approximately 24 hours after dosing.
Unabsorbed drug is excreted as both the free and acetylated forms via feces.
In patients with active ulcerative colitis or Crohn's disease receiving 500 mg of 5-ASA t.i.d. Also as adjunctive therapy in more extensive disease as well as for the prevention of relapse in distal ulcerative colitis. For the prevention of relapse in distal ulcerative colitis. In the management of ulcerative proctitis and as adjunctive therapy in more extensive distal ulcerative colitis. For the prevention of relapse.