Enzymic hydrolyzed chitosan was employed to prepare chitosan-tripolyphosphate and chitosan-polyphosphoric acid gel beads using a polyelectrolyte complexation method for the sustained-release of anticancer agent, 6-mercaptopurine (6-MP). pH responsive swelling ability, drug-release characteristics, and morphology of the chitosan gel bead depends on polyelectrolyte complexation mechanism and molecular weight of the enzymic hydrolyzed chitosan. The complexation mechanism of chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution was ionotropic crosslinking or interpolymer complex, respectively. The drug-release patterns of all chitosan gel beads in pH 6.8 seemed to be diffusional based, which might be in accordance with the Higuchi model, whereas release profiles of the chitosan-tripolyphosphate gel beads in pH 1.2 medium seemed to be non-Fickian diffusion controlled due to the swelling or matrix erosion of the beads. The rate of 6-MP releasing from chitosan-tripolyphosphate or chitosanpolyphosphoric acid gel matrix were significantly increased with the decreased molecular weight of enzymic hydrolyzed chitosan. However, the dissolution rates of 6-MP entraped in chitosan-tripolyphosphate and chitosan-polyphosphoric acid gel matrix were significantly slower than the dissolution rate of the original drug. These results indicate that the chitosan-polyphosphoric acid gel bead is a better polymer carrier for the sustained release of anticancer drugs in simulated intestinal and gastric juice medium than the chitosantripolyphosphate gel beads.
Chitosan tablets containing theophylline were prepared by directly compressing the wet or dry blended polymer-drug powders. The effects of the viscosity and swelling ability on the release rates of drugs were examined. The theophylline releasing rates of tablets prepared by polymer-drug wet blending increase with a decrease in the viscosity of the blending chitosan solution. On the other hand, the swelling ability of the polymer greatly influences the release kinetics of the tablets prepared by polymer-drug dry blending. Tablets prepared by both polymer-drug wet and dry blending were acid-nonresisted. Tablets in simulated gastric fluid disintegrated quickly, and the drugs were released within four hours. To retard the disintegrated rate of chitosan tablets in acid medium, interpolymer complex of chitosan with anionic polyelectrolyte (alginate) is needed. By this treatment, the swelling and erosion rate of the chitosan tablets could be reduced, then controlling the release rate of the theophylline can be achieved. Drug release mechanism of the various tablets were investigated by the model of Peppas; in addition, a nuclear magnetic resonance imagine microscopy is also introduced to examine the swelling or diffusion mechanism of various tablets.
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