Lateral iontophoretic solute transport in skin

Purpose, The lateral iontophoretic transport of three solutes (sodium, ethanolamine, lidocaine) from an active electrode through skin and other tissues to an indifferent electrodes was investigated. Methods, Anodal epidermal iontophoresis was carried out on an in vivo rat model using constant direct current of 0.38 mA/cm(2). Cells were fixed on the epidermis of anesthetized rats at distances of adjacent, 3 cm and 7 cm apart. After iontophoresis, tissues were dissected at I cm intervals between the electrodes. Concentrations of the radiolabelled solutes in tissues were determined by liquid scintillation counting or gamma counting. Results. The concentration of each solutes in the epidermis, dermis and other tissues was found to decrease in an exponential manner with lateral distance from the active electrode to the indifferent electrode. The detectable lateral distance for ethanolamine and lidocaine was less than 2 cm from the donor sites, at which distance the concentrations were not significantly different to those found in the corresponding contralateral site. The lateral drift velocities for all solutes in the epidermis and dermis were consistent with diffusivities of the order of 10(-6) cm(2)/s. The drift velocity of sodium was greater than either lidocaine or ethanolamine. Conclusions. The decline in solute concentration with lateral distance is mainly due to clearance from the site of application by the skin's microcirculation and decreases with distance from the active electrode until a baseline concentration, similar to the contralateral tissue concentration is reached.