Microemulsions--modern colloidal carrier for dermal and transdermal drug delivery

Microemulsions are modern colloidal drug carrier systems. They form spontaneously combining appropriate amounts of a lipophilic and a hydrophilic ingredient, as well as a surfactant and a co-surfactant. Due to their special features, microemulsions offer several advantages for pharmaceutical use, such as ease of preparation, long-term stability, high solubilization capacity for hydrophilic and lipophilic drugs, and improved drug delivery. The article summarizes the level of research with respect to dermal and transdermal application. A large number of in vitro as well as some in vivo studies demonstrated that drugs incorporated into microemulsions penetrate efficiently into the skin. The enhancing activity seems to be attributable to a variety of factors depending on the composition and the resulting microstructure of the formulations. However, an extended use in practice depends on the choice of well-tolerated ingredients, mainly surfactants, and the restriction of their amounts in order to guarantee skin compatibility.