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Controlled drug delivery technology is concerned with systematic release of a pharmaceutical agent to maintain a therapeutic level of the drug in the body for a sustained period of time. Various different approaches are used to develop controlled drug delivery systems. One such approach is using microspheres as carriers for drugs. Due to its small size they are widely distributed throughout the gastrointestinal tract which improves drug absorption and reduces side effects due to localized build-up of irritating drugs against the gastrointestinal mucosa. There are many methods for preparation of microspheres. Among them, ionotropic gelation method is one. The aim of the present work was formulation and evaluation of microspheres by ionotropic gelation method using sodium alginate as polymer and Cacl2 as cross-linking agent. Sodium alginate is biodegradable natural polymer with a great potential for pharmaceutical applications due to its good biocompatibility and non-toxicity. Cacl2 is also called a common salt which is made up of calcium and chlorine. Metformin hydrochloride was selected as a model drug. Metformin hydrochloride microspheres were prepared by dropping the drug containing solution sodium alginate. The droplets instantaneously formed gelled spheres by the ionotropic gelation technique. The microspheres were characterized by their percentage yield, morphology, particle size, swelling studies, encapsulation efficiency and in vitro drug release rate. Release studies were done in buffer (pH 1.2) and subsequently in buffer (pH 6.8). The release of drug from microspheres was greatly affected by drug concentration, polymer …