Topical delivery of pharmaceutical and cosmetic macromolecules using microemulsion systems

Microemulsions are transparent, thermodynamically stable colloidal systems. Over the recent years, they have been increasingly investigated due to their potential as skin delivery vehicles for a wide range of drug molecules. The nanoscale particle size and the specificity of microemulsion components are the main features determining the skin permeation process. However, in order to effectively cross the skin barrier, the active substance itself should also meet a number of requirements, such as relatively small molecular weight, high lipophilicity with certain polarity as well as a specific partition coefficient. This review focuses on recent advancements in topical microemulsion systems related to the transport of active ingredients into the skin, including those with high molecular weight and high polarity. Selected studies have shown that permeation of therapeutic macromolecules can be increased by the correct (i.e. tailored to a specific drug) design of the microemulsion. The degree of skin penetration as well as the kinetics and the site of drug release can be controlled by appropriate qualitative and quantitative selections of penetration promoters (microemulsion components), the structure of microemulsion and its viscosity. The drug-carrier interactions can also affect the effectiveness of microemulsion formulation. These relations have been described and evaluated in this review article.