Caracterização estrutural, vibracional e térmica da azitromicina dihidratada em função da temperatura

Abstract

Azithromycin (AZM) is an antibiotic used in the treatment of bacterial infections and is in the national list of essential medicines. The AZM has different crystalline forms that depend on the conditions under which the drug is submitted and which present variations in its final properties. Thus, to study the possible structural modifications of AZM, as well as the conditions in which these occur, is necessary for the quality control. This work aimed to perform the thermal, structural and vibrational characterization of azithromycin dihydrate (AZM-DH) as a function of temperature. In order to do so, the drug was acquired in its pure form and X-Ray Diffraction techniques were used by the powder method (DRXP), Raman Spectroscopy (ER), Thermogravimetry (TG) and Simultaneous Differential Thermal Analysis (DTA) and Exploratory Calorimetry Differential (DSC), in order to trace the starting profile. Subsequently the structural changes were investigated using DRXP and ER as a function of temperature (25 to 140 ° C). The TG curve indicated that the material has thermal stability up to about 51 ° C. After this temperature the material underwent mass loss to about 104 ° C, attributed to dehydration, and another loss starting at 188 ° C, attributed to decomposition. The DTA and DSC curves resemble each other, initially presenting an extensive endothermic event (~ 54 ° C) attributed to dehydration of the material, followed by an exothermic event (~ 96 ° C) attributed to the crystallization of an anhydrous phase and then a new endothermic event (~ 116 ° C) characteristic of material melting. Analysis of DRXP as a function of temperature revealed that the structure of the material is stable to about 70 ° C, but from this temperature the AZM-DH undergoes changes in the reflections of the Bragg peaks indicating phase transformation during dehydration. When reaching the temperature of 115 ° C the characteristic peaks of AZM-DH decay drastically of intensity, giving rise to the new peaks referring to a new anhydrous phase of the material. The ER technique as a function of temperature showed thermal stability in the vibrational modes of the material up to the 77 ° C level, except for the water vibration modes (3494 and 3558 cm -1). It was concluded that AZM-DH undergoes dehydration and passes to a new crystalline anhydrous phase, then to its amorphous phase and then fused. The results obtained can serve as parameters for the quality control of the material with highlight for Raman spectroscopy.