The aim of this study was to investigate the solid dispersion phase behavior of s- or rs-ibuprofen in stearic acid. By means of thermal analysis, we have demonstrated the total immiscibility, in solid state, of the corresponding binary mixtures. This indicates that no specific interactions exist between the chosen excipient and active pharmaceutical ingredient (API) that lead to eutectic systems. Furthermore, based on calorimetric and X-ray diffraction experiments, we have showed that upon cooling of the molten state, only stearic acid recrystallizes in the presence of s-ibuprofen, whereas a quaternary phase mixture is obtained for the racemic ibuprofen/stearic acid preparation. The solubility of stearic acid in s-ibuprofen liquid in all proportions was also determined. Overall, the results presented here offer an approach for the study of API/excipient interactions.
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