Chitosan is an abundant natural based polymer, obtained by alkaline N-deacetylation of chitin. The physical and chemical properties of chitosan, such as inter and intramolecular hydrogen bonding and the cationic charge in acidic medium, makes this polymer attractive for the development of conventional and novel pharmaceutical products. So far, a number of chitosan based colloidal systems have been revealed as very promising carriers for bioactive molecules. Being a bioadhesive polymer and having antibacterial activity, chitosan is a good candidate for oral cavity drug delivery. Also, because of its favourable biological properties such as nontoxicity, biocompatibility, and biodegradability, chitosan is a promising candidate for the enhancement of absorption of drugs using a buccal delivery system. Chitosan microspheres can reside longer in the stomach and allow for stomach-specific drug delivery. Chitosan acts as an absorption enhancer in the intestine by increasing the residence time of dosage forms at mucosal sites, inhibiting proteolytic enzymes, and increasing the permeability of protein and peptide drugs across mucosal membranes. Chitosan can be degraded by the microorganisms, which are present in the colon. Therefore, this polymer could have promising application in a colonspecific drug delivery. A number of in vitro and in vivo studies showed that chitosan is a suitable material for efficient non-viral gene and DNA vaccine delivery. As a result of the physical, chemical, and biological properties, chitosan has been used in many different formulations for drug and gene delivery in the gastrointestinal tract.
