Design of a drug delivery system with bimodal pH dependent release of a poorly soluble drug

A delivery system which provides bimodal pH dependent release of poorly water soluble carvedilol in gastric and intestinal environment was designed. Preparation of solid dispersion with porous silica ensured a significantly higher dissolution rate of carvedilol in acidic and alkaline media in comparison to pure drug, while granulation of that solid dispersion with enteric polymer dispersion resulted in diminished immediate release in acidic media and fast release of the remaining drug in alkaline media. The ratio in quantities of first vs. second release was controlled with amount of enteric polymer dispersion used for granulation process. Desired 25 mg release of carvedilol at pH values 1.2 and 6.8 was achieved when 1.80 g of polymer per 1.0 g of solid dispersion (drug to silica ratio= 0.25 g : 2.0 g) was used.