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  • Author or Editor: Márcia Pinto x
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Abstract  

Nitroimidazoles are heterocycle imidazoles with a nitrogen group incorporated in its structure. The objective of this study was to develop a model to characterize possible interactions between active substances and excipients using: Thermogravimetry, Differential Thermal Analysis, Differential Scanning Calorimetry, and DSC coupled to photovisual system. It was used three nitroimidazoles (metronidazole, secnidazole, and tinidazole) and two types of microcrystalline cellulose with different particle size (Microcel and Avicel). The binary mixtures were prepared in proportion (w/w) 1:1 (nitroimidazole:excipient). Thermogravimetric data demonstrated that the tinidazole was the nitroimidazole with better uniformity. The nitroimidazoles obeyed the zero order kinetic reaction, evidencing its vaporization processes. Differential thermal analysis data showed nitroimidazoles compatibility with the different microcrystalline celluloses studied, showing that microcrystalline celluloses stabilized the active substances. Calorimetric data of secnidazole showed two melting points, characteristic of the polymorphs presented in raw material. The vaporization constants values of nitroimidazoles studied were secnidazole > metronidazole > tinidazole and for the binary mixtures these values followed the order tinidazole > metronidazole ≥ secnidazole.

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Abstract  

This article had studied the thermal characterization of the raw material and different fluconazole crystals, obtained through recrystallization with different solvents using thermoanalytical techniques (TG, DTA, DSC-50, DSC Photovisual, DSC-60) and Pyr-GC/MS. The results confirmed that the fluconazole volatilizes without decomposition until 250 °C. Pyr-GC/MS showed hexachlorobenzene like impurities in fluconazole raw material.

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Journal of Thermal Analysis and Calorimetry
Authors: Ana Santos, I. Basílio, F. de Souza, A. Medeiros, Márcia Pinto, D. de Santana, and R. Macêdo

Abstract  

Thermal analysis is an essential analytical tool in development of new formulations as well as to study the interaction between drugs and excipients. This work aims to investigate the possible interactions between metformin and excipients as microcrystalline cellulose (Microcel MC101®), starch sodium glycolate (Explosol®), sodium croscarmellose (Explosel®), PVP K30, magnesium stearate, starch and lactose, usually employed in pharmaceutical products. TG, DSC and DTA techniques were used for the thermal characterization to track if the thermal properties of the drug substance were modified in the mixture. Disregard of the starch and lactose systems, no changes in thermal behavior of mixtures were found. Thermogravimetric studies (TG) of metformin and its binary mixtures showed different thermal behavior.

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Journal of Thermal Analysis and Calorimetry
Authors: Antonilêni Medeiros, Ana Santos, F. de Souza, J. Procópio, Márcia Pinto, and R. Macêdo

Abstract  

Stability of drugs and products has a great practical interest, which is facing to strict regulation. Thermal studies, besides the determination of the thermal properties of the investigated product allow the verification of possible interactions between the drug substances and excipients. The objective of this work was to obtain solid pre-formulates of paracetamol (PC) by spray drying (SPDR), as well as to investigate their thermal behavior. Dynamic and isotherm TG, conventional DSC and DSC-photovisual coupled methods were used to characterize the conventional and pre-formulated mixtures obtained by SPDR. The results of both DSC investigations showed slight alterations in melting temperatures, which suggests incompatibilities. The TG decomposition data of the mixtures evidenced that the dry process via SPDR leads to stability enhancement of the pre-formulated mixtures.

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Journal of Thermal Analysis and Calorimetry
Authors: Agna Hélia de Oliveira, Elisana Afonso de Moura, Márcia Ferraz Pinto, José Valdilânio Virgulino Procópio, Valmir Gomes de Souza, Fábio Santos de Souza, and Rui Oliveira Macêdo

Abstract

This work studied the thermal characterization of the pentoxifylline raw material through thermoanalytical techniques (TG, DSC, DSC-photovisual) and analysis of degradation products by Pyr-GC/MS. The picture obtained with DSC-photovisual showed the total vaporization of pentoxifylline at 230.0 °C. The TG dynamical curve presented only one step for the loss of mass evidencing to be a kinetic process of zero order reaction. The pyrograms obtained for pentoxifylline sample in the solid state and solution in the temperatures of 250.0, 300.0, and 400.0 °C, showed only one peak identifying the pentoxifylline.

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