Chitosan dispersed system for colon-specific drug delivery.

A chitosan dispersed system (CDS), which was composed of active ingredient reservoir and the outer drug release-regulating layer dispersing chitosan powder in hydrophobic polymer, was newly developed for colon-specific drug delivery. An aminoalkyl methacrylate copolymer RS (Eudragit) RS) was selected as a hydrophobic polymer because it is hardly dissolved in acidic medium in which easily dissolves chitosan. In order to obtain the bi-functional releasing characteristics, i.e. time dependent and site specific, capsules containing the active ingredient (Drug Capsules) were coated by the chitosan dispersed hydrophobic polymer, resulting in CDS Capsules. The release rate could be controlled by changing the thickness of the layer. Furthermore, for colon-specific drug delivery, an additional outer enteric coating was necessary to prevent the drug release from CDS Capsules in the stomach, since chitosan dispersed in the layer dissolves easily under acidic conditions. Resultant enteric-coated CDS Capsules reached the large intestine within 1-3 h after oral administration and they were degraded at the colon in beagle dogs.