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Despite having good efficacy in the treatment and prevention of tuberculosis, the administration of rifampicin (RIF) can cause serious side effects, resulting from the prolonged use of this substance. Thus, it is necessary to seek new systems for administering tuberculostatic drugs, to avoid unwanted adverse effects, increase their bioavailability and, consequently, improve their therapeutic efficacy. The present work describes the achievement of a pH-responsive system for RIF, using palygorskite, a fibrous clay mineral, as a nanocarrier. To evaluate the influence of some operational variables on the drug adsorption process, a 2 4 factorial experimental design was used. The experiment using a maximum concentration (0.125 mg/mL), lower mass of PAL (300 mg), and lower pH (pH 2) was more efficient compared to other experiments, resulting in a higher dose of the incorporated drug, equivalent to 33.62 mg/g. To elucidate the mechanism of interaction between the materials, the hybrid obtained was characterized by different characterization techniques (Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry/derived thermogravimetry, zeta potential, scanning electron microscopy, and dispersive energy spectroscopy). In addition, kinetic models and adsorption isotherms were applied to the experimental data. Through in vitro release studies, it was possible to verify the effectiveness of the pH-dependent system obtained. The adjustment of experimental release data to the theoretical model of Higuchi indicated that the release of rifampicin occurs in a prolonged way from the palygorskite.

In vitro dissolution tests are an extremely important tool in the development and quality control of drugs, making it possible to evaluate the performance or efficiency of the pharmaceutical form in releasing the active substance through the amount dissolved in the dissolution medium when the product is subjected to specific equipment. In this sense, the main objective of the present study was to evaluate the release of ascorbic acid in prolonged release commercial vitamin C tablets by dissolution tests. Ascorbic acid and drugs of two different brands were characterized using the techniques of Molecular Absorption Spectroscopy in the Region of Infrared (IR), Thermogravimetry/Derived Thermogravimetry (TG/DTG) and Differential Scanning Calorimetry (DSC). The in vitro dissolution tests were performed in a dissolver with a paddle apparatus at a temperature of 37°C (± 0.5°C), employing 900 mL of ultrapure water as the dissolution medium and a stirring speed of 50 rpm. The ascorbic acid dissolved in the aliquots of dissolution media obtained during the tests were quantified using the UV-Vis Molecular Absorption Spectroscopy technique. From the dissolution profiles, it was observed that the formulations of both brands promoted a prolonged release of ascorbic acid. The brand drug A dissolved about 67% of the active principle in about 360 minutes. The brand drug B, however, dissolved about 72% at the same dissolution time. Release kinetics was evaluated using kinetic models such as order zero, first order and Higuchi. The model that best fit the experimental data was that of Higuchi.

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