Understanding the relationship between wettability and dissolution of solid dispersion.

Improved wettability has been ascribed to one of the important mechanisms for enhanced dissolution of solid dispersions. But its relationship with dissolution has not been closely studied to date. In this study, solid dispersion of simvastatin (SV) and polyvinylpyrrolidone (PVP) was prepared without and with sodium dodecyl sulfate (SDS) incorporated, respectively. The dissolution, contact angle and water absorption rate of these solid dispersions were measured to elucidate the relationship between wettability and dissolution. An abrupt increase of dissolution was observed when PVP amount exceeded a critical value. Contact angle was decreased with increasing of PVP amount. And the dissolution efficiency of the solid dispersion was increased with the decreasing of the contact angle, which was divided by a critical angle of 40.8° into two linear parts. The result was validated in the dissolution of SDS incorporated solid dispersions. Contact angle correlated well with water absorption rate. A critical water absorption rate, with value of 0.535 μL/min, was also observed for the transition of dissolution efficiency. In conclusion, both contact angle and water absorption rate are good indicators for dissolution transition of solid dispersion, which show great potential in formula screening of solid dispersion.