Studies of chitosan/organic acid/Eudragit® RS/RL-coated system for colonic delivery

Prednisolone (PDS) beads were coated sequentially with (i) innermost hydrophobic layer of Eudragit® RS/RL, (ii) middle drug release-triggering layer of chitosan, organic acid and Eudragit® RS/RL, and (iii) outermost enteric coating layer. Continuous dissolution studies were carried out in artificial gastric fluid (pH 1.2), followed by intestinal fluid (pH 6.8), and finally in colonic fluid (pH 4 and 6) with and without β-glucosidase. While drug release was prevented in the gastric and small-intestinal fluids, a continuous release was observed in the colonic fluid. Succinic acid provided the fastest rate of release in the colonic fluid compared to citric, tartaric or malic acid. A combined mechanism of drug release is proposed, which considers the swelling of chitosan and Eudragit® RS/RL in the presence of succinic acid possibly via electrostatic interaction between the amine groups of chitosan/quaternary ammonium groups of Eudragit® RS/RL and the carboxyl groups of succinic acid in aqueous medium. The results of plasma pharmacokinetic studies in Sprague–Dawley rats showed that the developed system provided a significant delay (Tmax 9.3 h) in the absorption profile of PDS compared with simple enteric-coated (Tmax 4 h) or powder (Tmax 1 h) formulation that was taken as proof for the colon-targeted delivery.