Thermal compatibility between hydroquinone and retinoic acid in pharmaceutical formulations

Thermogravimetry (TG) and differential scanning calorimetry (DSC) are used in pharmaceutical studies for characterization of drugs, purity, compatibility of formulations, identification of polymorphism, evaluation of stability, and thermal decomposition of drugs and pharmaceutical formulations. Hydroquinone (HQ) and products containing HQ have been widely used as depigmentation agents for lightening the skin. Retinoids are compounds that have the basic core structure of vitamin A and its oxidized metabolites, or synthetic compounds that share similar mechanisms of action as naturally occurring retinoids. Depigmentants and excipients were analyzed by TG and DSC. The dynamic thermogravimetric curves were obtained on a SHIMADZU thermobalance, model DTG-60, using an alumina crucible, at the heating rate of 10 °C min−1, in the temperature range of 25–900 °C, under an atmosphere of nitrogen at 50 mL min−1. The sample's mass was 10 ± 0.05 mg. The DSC curves were obtained using Shimadzu calorimeter, model DSC-60, using aluminum crucible, at the heating rate of 10 °C min−1, in the temperature range of 25–400 °C. The thermogravimetric and calorimetric curves were analyzed using TASYS software SHIMADZU. In this study were found the interaction between retinoic acid (RA) and the following excipients: cetyl alcohol(CA), cetostearyl alcohol (CTA), glycerin(GLY), and dipropylene glycol (DPG), and that between HQ and the excipient, DPG. Therefore, additional studies are necessary to evaluate final formulations. Thermal analysis is an effective and reliable technique that can be used in the control of raw materials and pharmaceutical products, and for evaluating their employment potential in the development and characterization of products.