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Purpose: To demonstrate a very effective and easy way of stabilization of amorphous indomethacin (IMC) by preparing binary mixtures with octaacetylmaltose (acMAL). In order to understand the origin of increased stability of amorphous system inter- and intramolecular interactions between IMC and acMAL were studied., Methods: The amorphous IMC, acMAL and binary mixtures (IMC-acMAL) with different weight ratios were analyzed by using Dielectric Spectroscopy (DS), Differential Scanning Calorimetry (DSC), Raman Spectroscopy, X-ray Diffraction (XRD), Infrared Spectroscopy (FTIR) and Quantitative Structure-Activity Relationship (QSAR)., Results: Our studies have revealed that indomethacin mixed with acetylated saccharide forms homogeneous mixture. Interestingly, even a small amount of modified maltose prevents from recrystallization of amorphous indomethacin. FTIR measurements and QSAR calculations have shown that octaacetylmaltose significantly affects the concentration of indomethacin dimers. Moreover, with increasing the amount of acMAL in the amorphous solid dispersion molecular interactions between matrix and API become more dominant than IMC-IMC ones. Structural investigations with the use of X-ray diffraction technique have demonstrated that binary mixture of indomethacin with acMAL does not recrystallize upon storage at room temperature for more than 1.5 year. Finally, it was shown that acMAL can be used to improve solubility of IMC., Conclusions: Acetylated derivative of maltose might be very effective agent to improve physical stability of amorphous indomethacin as well as to enhance its solubility. Intermolecular interactions between modified carbohydrate and IMC are likely to be responsible for increased stability effect in the glassy state.

Differential scanning calorimetry (DSC), broadband dielectric (BDS), and Fourier transform infrared (FTIR) spectroscopies as well as theoretical computations were applied to investigate inter- and intramolecular interactions between the active pharmaceutical ingredient (API) indomethacin (IMC) and a series of acetylated saccharides. It was found that solid dispersions formed by modified glucose and IMC are the least physically stable of all studied samples. Dielectric measurements showed that this finding is related to neither the global nor local mobility, as the two were fairly similar. On the other hand, combined studies with the use of density functional theory (DFT) and FTIR methods indicated that, in contrast to acetylated glucose, modified disaccharides (maltose and sucrose) interact strongly with indomethacin. As a result, internal H-bonds between IMC molecules become very weak or are eventually broken. Simultaneously, strong H-bonds between the matrix and API are formed. This observation was used to explain the physical stability of the investigated solid dispersions. Finally, solubility measurements revealed that the solubility of IMC can be enhanced by the use of acetylated carbohydrates, although the observed improvement is marginal due to strong interactions.