Effect of core modification on the release of chlorpheniramine maleate from ethylcelulose and cellulose acetate propionate microcapsules

ABSTRACT

Chlorpheniramine maleate [CPM] was microencapsulated using ethylcellulose [EC] and cellulose acetate propionate [CAP] as polymeric drug carriers. Phase separation technique induced by non-solvent addition was used in preparing the microcapsules. Conditions for microencapsulating the drug were determined by constructing phase diagrams for both EC-toluene-cyclohexane and CAP-toluene-cyclohexane systems. At 3% EC in toluene 50% cyclohexane was found to be suitable to prepare hard wall microcapsules while, this concentration was 40% in case of 6% CAP in toluene. Modification of the crystalline shape of the drug was applied to facilitate polymer deposition. The physical properties, drug incorporation efficiencies of the prepared microcapsules were also greatly improved when modified spherical crystals of CPM rather than fine powder were encapsulated. The release profile of the drug from microcapsules was dependent on shape of core, type of polymer, pH of dissolution media. Generally dissolution was characterized by an initial rapid release followed by a slow one. At dissolution media of pH 1.2 drug release was slow compared with release at pH 7.2 and the release from CAP microcapsules was slower than that from EC microcapsules. This could be attributed to the low acid solubility of CPM and enteric coating property of CAP. On the other hand, at pH 7.2 initial release was higher than in pH 1.2 and the release was fast in case of CAP compared with that for EC. In all cases microcapsules containing spherical cores showed slow and uniform drug release compared with that containing unmodified cores. Further coating of the prepared microcapsules with chitosan caused more release retardation with a change in release kinetics from non-linear diffusion model into nearly constant release as shown with EC microcapsules