EFFECTS OF IONTOPHORESIS ON THE ELECTRICAL-PROPERTIES OF HUMAN SKIN IN-VIVO

Preliminary measurements have been made of the effect of iontophoresis on the electrical properties;of human skin in vivo. Skin impedance wa s measured as a function of frequency and as a function of applied dir ect (i.e., iontophoretic) current. The resistance of the skin was then determined from the accumulated impedance data in the normal way. Aft er the electrode chambers were attached to the forearm,and the pretrea tment 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. Curre nt application involved three current densities applied for three diff erent times (combined in such a way that three consistent amounts of t otal charge were delivered): 10 mu A/cm(2) for 10, 20 and 50 min; 50 m u A/cm(2) for 2, 4 and 10 min; and 100 mu A/cm(2) for 1, 2 and 5 min. Current application caused skin resistance to drop rapidly (at all cur rents, most of the change occurs within 10 seconds of beginning the cu rrent flow). At all current levels, the decrease in skin resistance le veled off at a value which was dependent upon current density, but som ewhat independent of time of current application: 10 mu A/cm(2)-approx . 45% of pretreatment value; 50 mu A/cm(2)-approx. 20% of pretreatment value; and 100 mu A/cm(2)-approx. 10% of pretreatment value. The time required for recovery of skin resistance increased with (a) increasin g lime of current application (at constant current density), and (b) i ncreasing current density. It is concluded that measurements of skin i mpedance (and derived values of skin resistance) in vivo, in man, can therefore provide direct electrical evaluation of the effects of ionto phoresis on the tissue. Such measurements, we believe, are of vital im portance with respect to the long-term application of iontophoresis as a method of drug delivery.