Concentration dependence of 5-aminosalicylic acid pharmacological actions in intestinal mucosa after oral administration of a pH-dependent formulation.

Asacol, a medication that delivers delayed release 5-aminosalicylic acid (5-ASA), is a useful therapeutic agent for inflammatory bowel disease (IBD), but the relationship between its pharmacological actions and intestinal concentrations has not been studied in detail. Therefore, our aim was to assess 5-ASA's pharmacological actions as a function of its concentration at its target site. We first evaluated 5-ASA's release profiles in vitro by the paddle method and found that Asacol starts to release 5-ASA at pH >= 7. Orally administered Asacol pharmacokinetic parameters were evaluated in dogs. Asacol's T(max) was much longer than that of he time-dependent release 5-ASA formulation. We also determined 5-ASA's distribution in the intestinal mucosa and found that it is effectively delivered there by Asacol. These results indicated that Asacol released 5-ASA in a pH-dependent manner, resulting in efficient delivery to the large intestine. We also compared the mucosal 5-ASA concentrations with the IC(50) values for scavenging free radicals or suppressing LTB(4) production. The 5-ASA concentration in the large intestine was higher than IC(50) values necessary to suppress inflammatory processes. We also report the release characteristics of Asacol and the targeted delivery of 5-ASA to affected sites in IBD patients.