DEVELOPMENT OF POLYMERIC MODIFIED RELEASE DRUG DELIVERY SYSTEMS

Although chitosan is a very promising biopolymer for use as carrier material in drug delivery systems, it has a limited capacity for controlling drug release from oral dosage forms due to its fast dissolution in the stomach. To overcome this disadvantage, chemical modifications such as co-polymerisation or derivatisation have been applied. However, this approach leads to the formation of new chemical entities with unknown toxicological profiles and a physical modification of the polymer is therefore rather preferred. Since chitosan is positively charged at pH values below its pKa value of 6.5, it spontaneously associates with negatively charged polyions in solution to form polyelectrolyte complexes. These chitosan based polyelectrolyte complexes exhibit favourable physicochemical properties with preservation of chitosan’s biocompatible characteristics. These polyelectrolyte complexes are therefore good candidate excipient materials for the design of different types of dosage forms. Some research projects are currently investigating the optimum ratio between chitosan and polycarbophil to form polyelectrolyte complexes that are most suitable for the manufacture of controlled release matrix drug delivery systems.  Other polymeric materials of natural origin are also investigated for use as excipients in modified release drug delivery systems such as mini-matrix type tablets and beads.