Ethosomes for skin delivery of ammonium glycyrrhizinate: in vitro percutaneous permeation through human skin and in vivo anti-inflammatory activity on human volunteers.

The aim of this work was the evaluation of various ethosomal suspensions made up of water, phospholipids and ethanol at various concentrations for their potential application in dermal administration of ammonium glycyrrhizinate, a useful drug for the treatment of various inflammatory-based skin diseases. Physicochemical characterization of ethosomes was carried out by photon correlation spectroscopy and freeze fracture electron microscopy. The percutaneous permeation of ammonium glycyrrhizinate/ethosomes was evaluated in vitro through human stratum corneum and epidermis membranes by using Franz's cells and compared with the permeation profiles of drug solutions either in water or in a water-ethanol mixture. Reflectance spectrophotometry was used as a non-invasive technique to evaluate the carrier toxicity, the drug permeation and the anti-inflammatory activity of ammonium glycyrrhizinate in a model of skin erythema in vivo on human volunteers. Ethosomal suspensions had mean sizes ranging from 350 nm to 100 nm as a function of ethanol and lecithin quantities, i.e., high amounts of ethanol and a low lecithin concentration provided ethosome suspensions with a mean size of approximately 100 nm and a narrow size distribution. In vitro and in vivo experiments were carried out by using an ethosome formulation made up of ethanol 45% (v/v) and lecithin 2% (w/v). The ethosome suspension showed a very good skin tolerability in human volunteers, also when applied for a long period (48 h). Ethosomes elicited an increase of the in vitro percutaneous permeation of both methylnicotinate and ammonium glycyrrhizinate. Ethosomes were able to significantly enhance the anti-inflammatory activity of ammonium glycyrrhizinate compared to the ethanolic or aqueous solutions of this drug. Some in vivo experiments also showed the ability of ethosome to ensure a skin accumulation and a sustained release of the ammonium glycyrrhizinate.