Microspheres

Microspheres are multiparticulate drug delivery systems which are prepared to obtain prolonged or controlled drug delivery to improve bioavailability, stability and to target the drug to specific site at a predetermined rate. They are made from polymeric waxy or other protective materials such as natural, semi synthetic and synthetic polymers. Microspheres are characteristically free flowing powders having particle size ranging from 1-1000 μm consisting of proteins or synthetic polymers. The range of techniques for the preparation of microspheres provides multiple options to control as drug administration aspects and to enhance the therapeutic efficacy of a given the drug. These delivery systems offer numerous advantages compared to conventional dosage forms, which include improved efficacy, reduced toxicity, improved patient compliance and convenience. Such systems often use macromolecules as carriers for the drugs. The present review highlights various types of microspheres, different methods of preparation, its applications and also various parameters to evaluate their efficiency. Microspheres are various types like Bioadhesive microspheres, Magnetic microspheres, Floating microspheres, Radioactive microspheres, Polymeric microspheres, Biodegradable polymeric microspheres, Synthetic polymeric microspheres and are prepared by methods like Spray Drying, Solvent Evaporation, Single emulsion technique, Double emulsion technique, Phase separation coacervation technique, Spray drying and spray congealing, Solvent extraction, Quassi emulsion solvent diffusion. Microspheres have wide range of applications because of controlled and sustained release.

Chitosan based microspheres containing were prepared by the emulsion cross linking method for nasal delivery of zolmitriptan. Nasal microspheres offer significant advantages over other type of drug delivery system. It modulates absorption characteristics of the drug by enhancing drug residence time in the nasal cavity and subsequently may increase bioavailability profile of administered drug. For the present study, Chitosan was selected as a mucoadhesive polymer. The microspheres were evaluated with respect to the particle size, production yield, encapsulation efficiency, shape and surface properties, drug and polymer interaction, mucoadhesive property, in vitro drug release. To optimize the microsphere formulation, 23factorial design was employed for investigating the effect of three factors, polymer concentration (chitosan), emulsifier concentration (Span 80) and cross-linking agent (gluteraldehyde) on response variable, which are encapsulation efficiency, in vitro drug release.

Microspheres are characteristically spherical and free flowing powders having particle size ranging from 1-1000 μm consisting of proteins or synthetic polymers. Microspheres are free flowing solid particle made up of biodegradable and non-biodegradable components Microspheric drug delivery system has wide range of application as it covers targeting the drug to particular site to imaging and helping the diagnostic features. Microspheres form an essential part of novel drug delivery systems. Microspheres reduce the dosing frequency and improve patient compliance by designing and evaluating Sustained Release microspheres for effective control of many chronic diseases. 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. A Microsphere has its drug dispersed throughout the particle i.e. the internal structure is a matrix of drug and polymeric excipients. The objective of this article is to emphasize on the principles underlying the development and evaluation of microspheres as a controlled and targeted drug delivery system.