A COMPARISON OF PULSED AND CONTINUOUS CURRENT IONTOPHORESIS

Na+ flux resulting from pulsed constant currents (50 μA amplitude with respect to virtual ground, 50% duty cycle at 10 Hz, 100 Hz, 1 kHz, and 10 kHz), with and without the presence of the analog switch (to obtain enhanced skin depolarization), and from constant voltage pulses (2 V amplitude with respect to ground, 50% duty cycle at 10 kHz, 100 kHz, and 1 MHz resulting in average currents which were < 150 μA) was measured and compared with the Na + flux obtained from an equivalent continuous current. All studies were performed with excised full thickness nude mouse skin which was bathed in a solution containing 25 mM HEPES and 0.133 M NaCl, maintained at pH 7.4 and at 37° C. The pulsed (constant current and constant voltage) iontophoretic Na + flux obtained without enhanced skin depolarization was shown to be equal to the Na+ flux obtained from an equivalent continuous current (P < 0.05). Enhanced depolarization of the skin during pulsed constant current iontophoresis resulted in a statistically significant (P < 0.05) decrease in Na+ flux relative to an equivalent continuous current only at 10 kHz. In addition, the application of all constant pulsed current protocols resulted in a decrease in the skin's low frequency impedance, a decrease which was greater than that obtained by skin hydration alone (P < 0.05). Finally, the voltage waveforms obtained across the skin during pulsed constant current iontophoresis could be experimentally and mathematically modelled by assuming the skin is a parallel resistor-capacitor combination. © 1990.