Although electrically assisted transdermal drug delivery has recently achieved a great deal of research attention, the precise anatomical pathway followed by these drugs through the stratum corneum has not been clearly defined.
Pigs are an accepted model for studying iontophoretic drug delivery in humans.
The purpose of this investigation was to visualize the pathway of ion transport by iontophoresing mercuric chloride. Although some compound penetrated the skin through appendageal pathways, the electron micrographs clearly revealed that mercuric chloride traversed the intact stratum corneum via an intercellular route. Precipitate was also localized in the outer membrane of the mitochondria in the viable epidermal cells, dermal fibroblasts, and capillaries, demonstrating transdermal delivery and systemic exposure to the mercury. These findings have implications for iontophoretic drug delivery, since they allow visualization of the functional pores predicted by mathematical models.