Delivery of large molecule drugs through the skin is an appealing goal, particularly for chronic uses where it would obviate the need for frequent injections. But normal skin is refractory to drugs with molecular weights greater than 400 daltons. Phospholipids would make attractive transdermal drug delivery agents except for one shortcoming: because they have a cylindrical shape, they tend to form prohibitively large, rigid aggregates that don't cross the skin.

IDEA, Innovative Dermal Applications GmbH, has developed technology to overcome that limitation. By adding cone-shaped molecules - usually biosurfactants - that come in between the phospholipids, a more flexible carrier wall is created that allows penetration through the skin. The resulting "ultradeformable" drug carriers can bring even large molecules through pores much smaller than the average diameter of the vesicle, according to Andreas Schätzlein, a scientist at IDEA.

These vehicles, called Transfersomes, were invented by Gregor Cevc, a founder of IDEA and a professor at the Technical University of Munich. His patent on the technology will issue in Europe in June.

Breaking the barrier

Transfersomes are applied to the skin as a clear, slightly opalescent wash, which then dries. The main barrier of the skin is the stratum corneum, which has