RESUMEN
Chitosan microspheres have been in the focus of increasing interest as polymeric drug carriers due to their appealing properties such as biocompatibility, biodegradability, low toxicity, mucoadhesion and relative low cost of production. Gel formation can be obtained by interactions of chitosan with low molecular we. counter-ions such as polyphosphates. However, one drawback of using this natural polysaccharide for oral controlled release dosage forms is its fast dissolution rate in the stomach. Since chitosan is positively, charged at low pH values [below its pKa value], it spontaneously associates with polyanions to form polyelectrolyte complexes [PEC]. These PEC these PEC exhibit favorable physicochemical properties with preservation of chitosan's biocompatible. characristics. These complexes are therefore good candidates for the design of colon-targeted dosage forms. Various techniques are used for preparing chitosan microspheres which have been reviewed. This review also includes factors that affect the release characteristics of drugs from chitosan microspheres