Development of chitosan-alginate microcapsules for colon specific delivery of metronidazole

The present study was aimed to develop and evaluate suitable chitosan-alginate microcapsules for colon-specific delivery of metronidazole for better treatment of amoebic colitis (important cause of death in the developing countries). Microcapsules were prepared by calcium chloride cross-linking method with different concentrations of sodium alginate and chitosan. Prepared microcapsules were treated for three different coatings with reduced molecular weight chitosan, guar gum and enteric coatings with cellulose acetate phthalate (CAP). Microcapsules were evaluated for size and morphology, thickness, strength and flexibility and drug content. In vitro drug release study was conducted by buffer change method to mimic GIT environment. For first two hours hydrochloric acid buffer (pH 1.2), next four hours phosphate buffer (pH 7.0) and last four hours phosphate buffer saline (pH 7.0) containing 33% of freshly prepared rat cecal content bubbling with CO₂ to simulate anaerobic conditions of colon, were used as elution medium. In morphological study, the chitosan membrane was found to be transparent, porous and continuous in nature. Chitosan concentrations significantly affected the strength and flexibility of membrane. Drug loading was decreased with increase in the weight of either encapsulating polymer or chitosan and different coatings. In vitro drug release was found to be marginally decreased with increasing chitosan and alginate concentrations. The coated microcapsules exhibited significantly retarded and colon specific drug release as compared to uncoated microcapsules. Among the three coatings, reduced molecular weight chitosan coating gave much lower drug release and exhibited high colon specificity.