Electrical properties of human stratum corneum and transdermal drug transport

Abstract

Complex impedance measurements have been used to study changes in electrical properties of human stratum corneum related to transdermal drug delivery. A careful determination of the effect of temperature revealed an activated process associated with the transport of charged species up to ca. 338 K. Above this temperature a drastic and irreversible decrease was observed in the resistance of the stratum corneum. This temperature, which has been identified by permeability studies and by a variety of biophysical measurements including differential scanning calorimetry (DSC), IR and EPR, corresponds to a transition caused by lipid melting. The changes in electrical properties occurring when stratum corneum was treated with chemical penetration enhancers also correlated well with results obtained using other techniques. Our measurements suggest that iontophoretically assisted transdermal drug delivery may cause less lipid structural alteration within the skin than would the use of such chemical penetration enhancers.