Water-in-oil microemulsions for effective transdermal delivery of proteins.

INTRODUCTION A water-in-oil microemulsion is a thermodynamically stable emulsion that has the capacity to 'hide' water-soluble molecules within a continuous oil phase. The very small size of the water droplets within the microemulsion means that these types of formulation can be applied topically to the skin, with the result that peptides and proteins can be delivered effectively into the dermal layer. AREAS COVERED This review discusses the general problems of peptide and protein delivery following topical application, and compares the possible routes of peptide and protein clearance and distribution within the body following topical administration. Several examples of successful peptide and protein delivery using microemulsions are discussed, in addition to the possible alterations in biological profiles following administration via this route. EXPERT OPINION Water-in-oil microemulsions present themselves as an effective means of topical delivery of peptides and proteins of all sizes, and in high doses. These formulations are a cheap, stable, pain-free means of delivery of peptides and proteins to the skin. An exciting area of potential development is the area of weight control management. The results using insulin, IGF-I and GHRP-6 given topically are particularly intriguing. Whether these results can be replicated in humans and whether the use of these drugs for potential treatment of obesity will be commercially viable will be particularly interesting.