Abstract
The different approaches for targeting orally administered drugs to the colon include coating with pH-dependent polymers, design of time-release dosage forms, and the utilization of carriers that are degraded exclusively by colonic bacteria. The aim of the present study was to develop a single unit, site-specific drug formulation allowing targeted drug release in the colon. Matrix tablets were prepared by wet granulation using cross-linked chitosan (ChI) and chondroitin sulfate (ChS) polysaccharides as binder and carrier. ChS was used to form polyelectrolyte complexes (PEC) with ChI, and its potential as a colon-targeted drug carrier was investigated. Indomethacin was used as a model drug. The ChI and ChS PEC was characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and powder X-ray diffraction studies (XRD). The matrix tablets were tested in vitro for their suitability as colon-specific drug delivery systems. FTIR demonstrated that the PEC forms through an electrostatic interaction between the protonated amine (NH(3)(+) group of ChI with the free carboxylate (COO(-)) group and sulfate (SO(4)(2-)) group of ChS. DSC and XRD indicated that the PEC has different thermal characteristics from ChI or ChS. The dissolution data demonstrates that the dissolution rate of the tablet is dependent upon the concentration of polysaccharide used as binder and matrix and time of cross-linking. The study confirmed that selective delivery of indomethacin to the colon can be achieved using cross-linked ChI and ChS polysaccharides.