Effect of iontophoresis on the electrical properties of human skin in vivo

Abstract

Preliminary measurements have been made of the effect of iontophoresis on the electrical properties of human skin in vivo. Skin impedance was measured as a function of frequency and as a function of applied direct (i.e., iontophoretic) current. The resistance of the skin was then determined from the accumulated impedance data in the normal way. After the electrode chambers were attached to the forearm, and the pretreatment resistance had stabilized, direct current was applied and the % change from baseline resistance was determined. At the end of current passage, the recovery of resistance was monitored for up to 4 h. Current application involved three current densities applied for three different times (combined in such a way that three consistent amounts of total charge were delivered): 10 p,A/cm2 for 10, 20 and 50 min; 50μA/cm2 for 2, 4 and 10 min; and 100μA/cm2 for 1, 2 and 5 min. Current application caused skin resistance to drop rapidly (at all currents, most of the change occurs within 10 seconds of beginning the current flow). At all current levels, the decrease in skin resistance leveled off at a value which was dependent upon current density, but somewhat independent of time of current application: 10μA/cm2 -approx. 45% of pretreatment value; 50 μA/cm2 -approx. 20% of pretreatment value; and 100 μA/cm2 - approx. 10% of pretreatment value. The time required for recovery of skin resistance increased with (a) increasing time of current application (at constant current density), and (b) increasing current density. It is concluded that measurements of skin impedance (and derived values of skin resistance) in vivo, in man, can therefore provide direct electrical evaluation of the effects of iontophoresis on the tissue. Such measurements, we believe, are of vital importance with respect to the long-term application of iontophoresis as a method of drug delivery.