Ionic Liquid Versus Prodrug Strategy to Address Formulation Challenges

Purpose A poorly water soluble acidic active pharmaceutical ingredient (API) was transformed into an ionic liquid (IL) aiming at faster and higher oral availability in comparison to a prodrug. Methods API preparations were characterized in solid state by single crystal and powder diffraction, NMR, DSC, IR and in solution by NMR and ESI-MS. Dissolution and precipitation kinetics were detailed as was the role of the counterion on API supersaturation. Transepithelial API transport through Caco-2 monolayers and counterion cytotoxicity were assessed. Results The mechanism leading to a 700 fold faster dissolution rate and longer duration of API supersaturation of the ionic liquid in comparison to the free acid was deciphered. Transepithelial transport was about three times higher for the IL in comparison to the prodrug when substances were applied as suspensions with the higher solubility of the IL outpacing the higher permeability of the prodrug. The counterion was nontoxic with IC 50 values in the upper μM / lower mM range in cell lines of hepatic and renal origin as well as in macrophages. Conclusion The IL approach was instrumental for tuning physico-chemical API properties, while avoiding the inherent need for structural changes as required for prodrugs. Graphical Abstract Stabilization of API in solution by Ionic liquid formation