No bioequivalence studies have been conducted for mesalamine because of differences in formulation. Based on U.S. Food and Drug Administration definitions for bioequivalence, none of these drugs can be classified as bioequivalent or therapeutically equivalent. No adequate comparative trials have been conducted with equivalent mesalamine doses to determine if any of the current formulations are superior in the treatment of ulcerative colitis. All of these mesalamine formulations are effective, but they differ with regard to where the drug is released in the intestinal tract, which may influence the outcome in some patients. Therefore, the selection of a mesalamine agent should be based on the results of the clinical trials, individual patient response, compliance issues, and price, until comparative clinical trials are published.