Usefulness of Low-Resistance Electrodes Used in Iontophoresis to Enhance Skin Permeability of Drugs

This study investigated how electrode design and electrical conditions influence iontophoretic transdermal drug delivery. A low-resistance silver electrode (Ag*) was developed to reduce interfacial resistance and improve the delivery of lidocaine hydrochloride (LID·HCl). In vitro permeation experiments were conducted using pig ear skin mounted on diffusion cells. Iontophoresis was applied under constant current, constant voltage, and battery-powered conditions. Ag* and conventional Ag electrodes were compared as anodes, with an Ag/AgCl cathode. Drug permeation and current profiles were measured over 8 h. Under constant current conditions, LID·HCl permeation through skin increased linearly with current density (r = 0.993). Enhanced permeation was also observed under constant voltage and battery-driven systems. The Ag* electrode produced higher current and greater drug permeation than the conventional Ag electrode at the same voltage due to its microstructured surface, which increased effective surface area and reduced charge-transfer resistance. Skin permeation was governed by current intensity. The Ag* electrode enabled efficient drug delivery even with simple battery systems, suggesting its potential for use in wearable transdermal delivery devices.