Abstract: 
Microspheres are characteristically free flowing powders consisting of proteins or synthetic polymers which are biodegradable in nature and ideally having a particle size less than 200 μm. A well designed controlled drug delivery system can overcome some of the problems of conventional therapy and enhance the therapeutic efficacy of a given drug. There are various approaches in delivering a therapeutic substance to the target site in a sustained controlled release fashion. One such approach is using microspheres as carriers for drugs. It is the reliable means to deliver the drug to the target site with specificity, if modified, and to maintain the desired concentration at the site of interest without untoward effects. This article aims to provide a comprehensive review of advantages, methods of preparation, mechanism, routs of administration, different types of microspheres based on natural and synthetic biodegradable polymers and application of biodegradable polymeric microspheres.

Keywords: Microspheres, Controlled Release, Polymers, Carriers, Target Site.