The microparticles have been utilized for prolonged and uniform drug release of a single dose in the gastrointestinal tract (GIT) and hence reducing the total dose required to elicit therapeutic activity, thereby avoiding the major side effects. The purpose of the present work is to prepare ethyl cellulose microparticles with high entrapment of zidovudine. The (water-in-oil)-in-oil emulsion solvent diffusion technique was used with or without external hydrophobic processing phase saturation with drug at various concentration for microparticles formulations. The prepared microparticles were evaluated with respect to entrapment efficiency, particle size, surface characteristics and in vitro release behavior. The process without external phase saturation produced spherical microparticles with 55 % zidovudine entrapment efficiency. The external phase saturation with 0.1 %, 0.2 % and 0.4 % w/v of drug induced the formation of microparticles with the entrapment efficiency of 60 %, 76 % and 98 %, respectively. The SEM photomicrographs of the freshly prepared microparticles revealed that the surface of the microparticles was smooth and nonporous and / or less porous as compared to the microparticles obtained without incorporation of drug in the external processing medium. A slight increase in yield values and decrease in particle size were observed with microparticles formulations with external phase saturation. The in vitro dissolution studies showed biphasic zidovudine release: the first one corresponds to a burst drug release and the second one to a constant drug release. It is concluded that zidovudine can be encapsulated in ethyl cellulose microparticles with high entrapment using saturated external hydrophobic phase with drug in (water-in-oil)-in-oil emulsion solvent diffusion technique.
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