SynopsisIt has been recognized that the vehicle in which a permeant is applied to the skin has a distinctive effect on the dermal and transdermal delivery of active ingredients. The cutaneous and percutaneous absorptions can be enhanced, e.g. by an increase in thermodynamic activity, supersaturation and penetration modifiers. Furthermore, dermal and transdermal delivery can be influenced by the interactions that may occur between the vehicle and the skin on the one hand, and interactions between the active ingredient and the skin on the other hand. Emulsions are widely used as cosmetic and pharmaceutical formulations because of their excellent solubilizing capacities for lipophilic and hydrophilic active ingredients and application acceptability. This review focuses, in particular, on the effect of emulsions on the dermal and transdermal delivery of active ingredients. It is shown that the type of emulsion (w/o vs. o/w emulsion), the droplet size, the emollient, the emulsifier as well as the surfactant organization (micelles, lyotropic liquid crystals) in the emulsion may affect the cutaneous and percutaneous absorption. Examples substantiate the fact that emulsion constituents such as emollients and emulsifiers should be selected carefully for optimal efficiency of the formulation. Moreover, to understand the influence of emulsion on dermal and transdermal delivery, the physicochemical properties of the formulation after application are considered. Ré suméOn sait que le véhicule dans lequel un perméat est appliqué sur la peau a un effet spécifique sur la libération dermique et transdermique des ingrédients actifs. Les absorptions cutanées et percutanées peuvent être augmentées, par exemple par une augmentation de l'activité thermodynamique, une super saturation ou la présence de modificateurs de pénétration. Ainsi, la libération dermique et transdermique peut être influencée par les interactions susceptibles de s'établir d'un côté entre le véhicule et la peau et de l'autre entre l'ingrédient actif et la peau. Les émulsions sont largement utilisées dans les formulations cosmétiques et pharmaceutiques du fait de leurs excellentes capacités de solubilisation des ingrédients actifs lipophiles et hydrophiles, et du fait de leur bonne tolérance. Cette revue traite, en particulier, des effets des émulsions sur la libération dermique et trans-dermique d'ingrédients actifs. On montre que le type d'émulsion (E/H par rapport à H/E), la granulomé-trie, l'émollient, les émulsifiants, autant que l'organisation des tensioactifs (micelles, cristaux liquides lyotropes) peuvent influencer l'absorption cutanée et percutanée. Des exemples justifient le fait qu'un choix soigné des constituants de l'émulsion comme les émollients et les émulsifiants peut optimiser l'efficacité de la formulation. En complément, pour comprendre l'influence de l'émulsion sur la libéra-tion dermique et transdermique, les propriétés physico-chimiques de la formulation après application sont étudiées.The effect of the vehicle on dermal and transdermal deli...

In this study the effect of 2 penetration modifiers, dimethyl isosorbide (DMI) and diethylene glycol monoethyl ether (DGME) on the skin delivery of hydroquinone (HQ), salicylic acid (SA) and octadecenedioic acid (DIOIC) was investigated. Ten percent DMI and DGME were separately formulated into oil-in-water emulsions containing 1.8% HQ, SA and DIOIC, respectively. Skin delivery and the flux across split-thickness human skin of the active ingredients were determined using Franz diffusion cells. An emulsion with 10% water incorporated instead of the water-soluble penetration modifiers served as a control. The study showed that neither 10% DMI nor 10% DGME significantly enhanced the skin permeation of the various lipophilic active ingredients or the uptake into the skin. It was hypothesized that the addition of the penetration modifiers to the emulsions not only enhanced the solubility of the various active ingredients in the skin but also in the formulation, resulting in a reduced thermodynamic activity and hence a weaker driving force for penetration. Therefore, the effect of DMI and DGME on the solubility of the active ingredients in the skin was counteracted by a simultaneous reduction in the thermodynamic activity in the formulation.

Ultimately, the choice between micro- and nanometer-sized delivery systems is not straightforward. However, if the fundamental differences in physical and chemical properties are considered, it can be much easier to make a rational choice of the appropriate drug delivery system size.

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