Drug salts and solubilization: modeling the influence of cyclodextrins on oral absorption

Substantial effort and resources are spent for the oral delivery of low solubility compounds using drug delivery technologies. Complexation using cyclodextrins (CDs) is one popular strategy used to enhance drug dissolution kinetics and solubility. In addition to delivery technologies, another common method of improving dissolution kinetics of a low solubility compound is to dose it as a salt. It is not often possible to anticipate how effective a technology such as CD will be in a certain formulation in improving drug absorption, leading to a trial-and-error based formulation process; simultaneous use of salt and complexation technologies increases the complexity of the system. A simple dynamic, systems-based model was developed for predicting the influence of CDs on oral absorption of a salt form of low solubility drug administered as a physical mixture with CD, and validated by in vitro experiments. Model predictions indicate that while CD is generally considered a solubilization technology, CD can enhance overall absorption of salt form drug mainly by decreasing the driving force for precipitation through binding free drug in solution. Modeling enabled examination of which physical and chemical properties result in oral absorption enhancement or decrement for drug salt administered as a physical mixture with CD.