Evaluation of zidovudine encapsulated ethylcellulose microspheres prepared by water-in-oil-in-oil (w/o/o) double emulsion solvent diffusion technique

The preparation of zidovudine-loaded ethylcellulose microspheres by w/o/o double emulsion solvent diffusion method with high entrapment capacity and sustained release is described. A mixed solvent system (MSS) consisting of acetonitrile and dichloromethane in a 1:1 ratio and light liquid paraffin was selected as primary and secondary oil phases, respectively. Span 80 was used as the secondary surfactant for stabilizing the external oil phase. Spherical free flowing microspheres were obtained. The prepared microspheres were characterized by entrapment efficiency, in vitro release behavior, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The drug-loaded microspheres showed 32 - 55% entrapment capacity. The in vitro release profile could be altered significantly by changing various processing and formulation parameters to give sustained release of drug from the microspheres. The DSC thermograms confirmed the absence of any drug-polymer interaction. SEM studies showed that the microspheres were spherical and porous in nature. The in vitro release profiles from microspheres of different polymer-drug ratios were best fitted to Higuchi model with high correlation coefficient and the n value obtained from Korsmeyer-Peppas model was ranged between 0.23 - 0.54. The drug release was found to be diffusion controlled mechanism.