6-mercaptonicotinamide-functionalized chitosan: a potential excipient for mucoadhesive drug delivery systems

Among mucoadhesive polymers, thiolated polymers showed to be superior over non-thiolated polymers. Recently a novel thiolated chitosan named chitosan-6-mercaptonicotinamide has been generated. Its heteroaromatic structure confers a pH-independent reactivity to the thiol group and introduces a hydrophobic entity in the hydrophilic polymer. Within this study the potential of this novel polymer as excipient for drug delivery systems was evaluated with a special focus on mucoadhesion. The highest coupling degree was 975 μmol thiol groups in reduced form per gram of polymer. Mucoadhesion was increased by at least 69-fold compared to unmodified chitosan. This chemical modification of chitosan, altered the water uptake of the polymer by lowering it up to 75 %. The new polymer was effective in stabilizing a matrix tablet compared to an unmodified chitosan tablet. Cumulative release studies from a matrix tablet comprising the newly synthesized chitosan showed controlled release of a hydrophilic macromolecular model compound (FD4). Furthermore, the polymer showed improved biodegradability. These advantageous features render chitosan-6-mercaptonicotinic acid a useful excipient for various drug delivery systems