Topical hydrogels with escin β-sitosterol phytosome and escin: Formulation development and in vivo assessment of antihyperalgesic activity.

The physicochemical properties, stability, in vivo antihyperalgesic activity, and skin irritation potential of the carbomer hydrogels with the new chemical entity escin β-sitosterol (ES) phytosome were characterized and compared with those containing escin. Physicochemical characterization of the hydrogels (performed 48 hr after preparation) included organoleptic examination, pH measurement, light microscopy, differential scanning calorimetry analysis and rheological tests. The obtained results showed that increasing concentration of the active substances within 1-5% affected the appearance (color and transparency) of the hydrogels, their pH, consistency, and rheological behavior. Unlike acidic escin, which was dissolved in the liquid phase of the pseudoplastic hydrogels E1-E5 and reduced their maximal apparent viscosity (η ), minimal apparent viscosity (η ), and hysteresis area (H) in comparison to the plain carbomer hydrogel, amphiphilic ES-enhanced η , η , and thixotropy of the hydrogels ES1-ES5, which is favorable for prolonged retention at skin surface. Evaluation of in-use stability of the hydrogels showed that organoleptic characteristics, flow behavior, and pH values could be preserved for 3 months under ambient conditions. The rat ear test results suggested that the hydrogels are safe to be used on human skin. Both escin and ES-loaded hydrogels exerted significant, concentration-dependent antihyperalgesic effect in inflammatory pain model in rats. ES-loaded hydrogels were significantly more effective than those loaded with escin. This is a first report on the antihyperalgesic effect of topically applied escin as well as ES in a model of inflammatory pain.