PREPARATION AND RELEASE PROPERTIES OF BIODEGRADABLE CHITIN MICROCAPSULES .2. SUSTAINED-RELEASE OF 6-MERCAPTOPURINE FROM CHITIN MICROCAPSULES

Chitin microcapsules are prepared using a simple desolvation or nonsol vent addition phase separation method with 6-mercaptopurine (6-MP) as a reference core. Chitin with a molecular weight about 400 000 is used to prepare different core loaded microcapsules. The drug release rate s of chitin microcapsules prepared by simple desolvation or nonsolvent addition method have different release profiles which are related to the rate of phase separation. With respect to the solubility parameter difference (Delta delta) value between solvent and nonsolvent, the re lease rate of 6-MP from microcapsules decreases with increasing Delta delta of the preparative system. The chitin beads show poor swelling p roperties and their release rates are pH-dependent. Sustained release of 6-MP from chitin microcapsules in low pH and neutral medium can be accomplished. To determine if the drug release from the polymer matrix is via a diffusion controlled or by an erosion controlled process, 6- MP release profiles of various chitin microcapsules degraded by lysozy me are investigated. The drug-release patterns of the chitin microcaps ules prepared by nonsolvent addition (acetone, n-propanol, n-butanol) and simple desolvation in acetone are not only diffusion but also lyso zyme digestion influenced. Whereas, by using water or ethanol as nonso lvent or desolvating agent, release profiles of the microcapsules prep ared by nonsolvent addition and the simple desolvation method seem to be little affected by enzyme degradation. These results indicate that chitin might prove useful as a polymer carrier for the sustained relea se of drugs.