Study of the Amorphous Glibenclamide Drug: Analysis of the Molecular Dynamics of Quenched and Cryomilled Material

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Abstract

Glibenclamide (GCM) is an oral hypoglycemic agent of the sulfonylurea group used in the treatment of non-insulin-dependent diabetes. Crystalline GCM is characterized by low bioavailability, which is attributed to its poor dissolution properties. It prompted us to prepare this drug in its amorphous form as a means to enhance its dissolution characteristics. Two different methods were used to convert crystalline GCM into the glassy form: quench-cooling of the melt and cryogenic milling. To monitor solid-state properties of the amorphous samples, X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), ultraperformance liquid chromatography (UPLC) and spectroscopy, and broadband dielectric spectroscopy (BDS) were applied. The results of UPLC separations along with associated infrared and NMR measurements unambiguously showed that the thermal degradation of the quenched GCM, as suggested in literature reports, does not occur. A similar analysis performed on the cryomilled material also did not indicate any chemical decomposition. On the other hand, both methods confirmed that the conversion to the amorphous form is connected with the amide−imidic acid tautomerism of the examined drug. Moreover it was shown that this transformation occurs regardless of the manner of amorphization. Finally, dielectric spectroscopy was employed to study the molecular dynamics of vitrified GCM. The analysis of the ε′′(f) in terms of the KWW function from the dielectric measurements revealed the existence of an “excess wing” attributed to the true Johari−Goldstein process based on Ngai’s coupling model. The dielectric properties of GCM obtained in the amorphous form both by rapid cooling of the melt and the cryogenic grinding of crystalline sample were also compared.

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