Non-invasive assessment of the effects of iontophoresis on human skin in-vivo

The stratum corneum (SC), the outermost layer of the skin, presents a formi dable barrier to transdermal drug delivery. As a result, different strategi es have been developed to enhance drug transport into and through skin. Ion tophoresis involves the application of a small electrical current which dri ves molecules across the skin and controls relatively well the rate of deli very. Although the technique has been widely investigated in-vitro, the eva luation of skin integrity in-vivo after iontophoresis is absolutely necessa ry for the future clinical application of this approach. This paper reviews the non-invasive biophysical techniques which have been used to assess the effects of current application on human skin in-vivo. Specifically, transe pidermal water loss, infrared spectroscopy, impedance spectroscopy and skin blood flow measurements are discussed. After first presenting the basic pr inciples of these methods, their application to the determination of SC bar rier function and skin integrity is addressed, and the criteria for selecti ng the most appropriate approach are considered.