In Situ Salification in Polar Solvents: a Paradigm for Enabling Drug Delivery of Weakly Ionic Drugs as Amorphous Solid Dispersion
Solubility challenge for a poorly water-soluble drug gets further intensified when it is weakly ionic because the most common solubility enhancement technique, salt formation, becomes less feasible. Salt screening for such drugs often concludes with either a difficult to crystalize salt or an unstable salt, leading the scientists to explore other solubility enhancement technique like amorphous solid dispersions which is comparatively costlier, time-consuming and may require use of hazardous organic solvents. Present study evaluated in situ salification in polar protic solvents for dissolving poorly water-soluble drug Itraconazole which is weakly ionic and not very amenable to formation of stable inorganic salts. Through systematic selection of solvents, counterions and polymers, an amorphous solid dispersion of drug salt was obtained. In vitro characterizations with polarized light microscopy (PLM), modulated differential scanning calorimetry (mDSC), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) confirmed the physical and chemical stability of the amorphous solid dispersion. In vivo pharmacokinetic study showed that the drug salt amorphous solid dispersion achieved 45 times higher plasma exposure compared to crystalline drug. This study provides one of the first data sets for the hypothesis that in situ drug salts can be utilized for manufacturing amorphous solid dispersions of weakly ionic drugs and leverages the solubility advantage of salts and amorphous state.