Amorphous Solid Solutions in Glassy Hydrogels for Enhancing the Delivery of Poorly Soluble Drugs

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One major challenge in oral drug delivery has been the low bioavailability of many crystalline compounds exhibiting poor solubility characteristics. Traditional methods for solubility enhancement involving solubilizing agents (e.g. co-solvents & surfactants) and particle size reduction have not always been successful. On the other hand, the creation of solid solutions (molecular dispersions) in soluble polymers has shown potential to be effective in enhancing the dissolution and oral bioavailability due to the higher solubility of the amorphous drug (supersaturation). However, the mechanisms of drug dissolution and release from amorphous solid solutions and their effect on the overall time evolution of supersaturation during dissolution are not well understood and have not been fully explored. In addition, physical instability of these systems during storage such as crystallization on aging has limited their success in commercial applications. Furthermore, no criterion exists in determining the threshold drug loading level above which crystallization may occur in these soluble polymers. Despite the ongoing interest in hydrogels as biomaterials and carriers for controlled drug release, the novel application of cross-linked glassy hydrogels for stabilizing the loaded drug in an amorphous state has not been fully investigated. Cross-linked hydrogels are more advantageous than soluble polymers in this regard since the three-dimensional network in the glassy state is more effective in preventing the crystallization of loaded amorphous drug. Experimental evidence suggests that solid solutions based on hydrogels can also avoid peaks and valleys in the kinetic solubility profiles normally associated with solid solutions based on soluble polymers, thereby achieving a more sustained drug supersaturation than conventional systems based on soluble polymers. We therefore propose to conduct an in-depth investigation of this hydrogel-based system and identify the optimal range of design parameters that can effectively inhibit the crystallization of loaded drug and maximize the supersaturation maintenance to enhance the delivery of poorly soluble drugs.