Development of Smart Semisolid Formulations to Enhance Retinoic Acid Topical Application

Retinoids play a very important role in the topical treatment of acne vulgaris. However, their use is restricted because of the limited photostability responsible for local adverse effects as erythema, dryness, itching, and stinging. In this way, the therapeutic efficacy of such molecules is strongly reduced, resulting, at the same time, harmful for the patient upon light exposure. Thus, a suitable technological strategy is necessary to increase retinoid stability in order to have a product both safe and efficacious. With this aim, new inorganic-organic hybrids based on tretinoin (retinoic acid, RET) and hydrotalcite-like compounds (HTlc) have been prepared and well characterized by X-ray powder diffraction, inductively coupled plasma spectrometry, thermal analyses, scanning electron microscopy, and UV-Vis spectrophotometric measurements. Such hybrids, namely, ZnAl-HTlc-RET and MgAl-HTlc-RET, were formulated as simple gels for topical use and submitted to further studies in order to evaluate their rheological properties, photostability, and RET release capability. The RET photostability resulted improved upon intercalation into HTlc, both in MgAl-HTlc and ZnAl-HTlc, as proved by the data acquired during irradiation of the sample at 366 nm. This strategy is suitable for the realization of safe, efficacious, and compliant topical formulations for acne treatment.