A novel polyelectrolyte complex (PEC) hydrogel for controlled drug delivery to the distal intestine

This work was aimed at preparing and evaluating a physically crosslinked hydrogel for the controlled release of diverse drugs to the distal intestine. A solution of fluorescein isothiocyanate dextran, MW 4400 Da (FD4), or a dispersion of micronized dexamethasone (DMS) was microencapsulated into a PEC hydrogel, composed of polycationic N-trimethyl chitosan (TMC) and polyanionic N-carboxymethyl chitosan (CMCh). A fine spray of a 1% CMCh solution containing 1% FD4 in solution or 0.1% DMS in dispersion was directed into a 2% TMC solution, then the resulting microcapsules (MCPS) were lyophilized. MCPS were analyzed by SEM and solid-state NMR. Drug release from MCPS was too fast, so these were compressed into matrices (weight 20 mg; diameter 6 mm; drug load 2.5%, with FD4, or 3.7%, with DMS) which were enteric coated. Drug release from matrices was studied simulating matrix transit across GI environments of different pHs, from stomach to proximal colon. The enteric film hindered release in stomach and proximal small intestine. After film dissolution at ileum pH, release occurred with a pattern described by the Peppas equation (n=0.6, with DMS; n=0.7, with FD4). As the pH changed from 7.4 to 6 (from ileum to ascending colon) MCPS were liberated from matrix surface. This phenomenon sustained the release rate. The present MCPS allow controlled doses of macromolecular or mi- croparticulate drugs being uniformly loaded into controlled-release matrices based on a physically crosslinked, biodegrad- able hydrogel.