Hydrocolloids and gels of chitosan as drug carriers

Abstract

Chitosan, a natural, biocompatible polymer, is becoming popular in dosage form design. In our study the design factors affecting the release of lidocaine and lidocaine chloride from chitosan hydrocolloids and gels were studied. In hydrocolloids a relatively high viscosity was found at low concentrations of chitosan caused by the increased effective volume of the polymer molecules, due to the reflection of the same charges in the chains. The drug release is slow and sustained, being influenced by the chitosan content. The mechanism of chitosan gel formation is not known exactly, but it is clear that for gel formation the length of the chitosan chains and the degree of reacetylation are responsible. The release profile of gels follows almost zero order kinetics. Also, the degree of reacetylation is responsible for the release behaviour. The rotational motion of nitroxides (Tempol, spin-labeled lidocaine) determined by EPR experiments showed practically equal rotational motion at different degrees of reacetylation. Thus, it was concluded that the free spaces, available for nitroxide rotation, were not changed significantly. The degree of reacetylation affects the translational diffusion more strongly.