Preparation and Evaluation in vitro of Usnic Acid Emulgel with Varying Concentrations of Propylene Glycol

Abstract

Usnic acid is one of the secondary metabolites found in lichens. Usnic acid has anti-inflammatory activity and is classified as class 2 in the Biopharmaceutical Classification System (BCS), with low solubility but high permeability. Therefore, a suitable delivery system is needed to enhance the release and penetration of usnic acid through the skin. Propylene glycol is a common component in topical formulations due to its humectant and penetration-enhancing properties, which can improve the release of active substances from the dosage form matrix. This research aims to develop and evaluate usnic acid emulgel preparations with varying propylene glycol concentrations and to determine their effects on physical characteristics, stability, and in vitro drug release. Methods: The research methods included the isolation and characterization of usnic acid, the formulation of an emulgel with varying propylene glycol concentrations (0%, 5%, 10%, and 15%), and the evaluation of physical properties, including organoleptic, homogeneity, pH, viscosity, spreadability, and stability through freeze-thaw tests. In addition, content determination and in vitro release tests were conducted using a Franz diffusion cell. . The results showed that all formulas met the requirements for a good topical preparation, with a pH within the skin range (4.5–6.5), homogeneity, and physical stability. Increasing the propylene glycol concentration decreased viscosity and improved spreadability and homogeneity. In vitro release tests showed that the formula with 15% propylene glycol produced the highest usnic acid release among the formulas. ). Conclusions: Variations in propylene glycol concentration significantly affected the characteristics and release of usnic acid from emulgel preparations. A 15% concentration was the optimal formulation for increasing the release of the active ingredient, with potential for further development as a natural-based topical anti-inflammatory preparation. There is an effect of varying propylene glycol concentrations on in vitro release.