Carvedilol dissolution improvement by preparation of solid dispersions with porous silica

Impregnation of porous SiO2 (Sylysia) with carvedilol from acetone solution was used to improve dissolution of this poorly water-soluble drug. Solvent evaporation in a vacuum evaporator and adsorption from acetone solution were the methods used to load various amounts of carvedilol into the Sylysia pores. The impregnated carriers were characterized using nitrogen-adsorption experiments, X-ray diffraction, wettability measurements, attenuated total reflectance FTIR spectroscopy and thermal analysis. The impregnation procedures resulted in a significant improvement of drug release compared to dissolution of pure carvedilol or its physical mixtures with Sylysia. The results showed that when the drug precipitated in a thin layer within the carrier the dispersion retained a high specific surface area, micropore volume, and drug-release rate from the solid dispersion. Increasing the amount of drug in the solid dispersion caused particle precipitation within the pores that decreased the carrier's specific surface area and pore volume and decreased the release rate of the drug. The results also suggest that the amorphous form of carvedilol, the improved wettability and weak interactions between the drug and carrier in the solid dispersion also contribute to improved dissolution of the drug from the dispersion. (c) 2011 Elsevier B.V. All rights reserved.