The aim of this study was to investigate whether hollow microspheres prepared from polymer blends of polyvinyl pyrrolidone (PVP) and ethyl cellulose (EC) could improve the vitro release behavior of the poorly water-soluble drug nifedipine. Hollow microspheres containing nifedipine were prepared by a solvent diffusion-evaporation method using various ratios of PVP and EC codissolved with drug in ethanol/ether (5:1, v/v). The hollow microspheres could float in release medium for more than 24 h, and floating capacities were not be influenced by mixing PVP. In vitro release profiles of hollow microspheres prepared using EC along showed an initial burst release to some extent, and the cumulative release percentage was less than 55% after 24 h. But, not only the slope but also the shape of the release curves was affected by using mixture of PVP and EC. What's more important, when the ratio (PVP/EC) increased to 1.5:8.5, the cumulative release percentage could be increased to 95.8%. Furthermore, the release rate of microspheres showed a zero order approximate dynamic model and could be expressed by the following equation: Q=3.78t+8.52 (r=0.990). Consequently, hollow microspheres prepared using polymer blends of PVP and EC (1.5:8.5, w/w) could be suitable for floating-type controlled-release delivery systems for the oral administration of nifedipine.
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