Theoretical model of iontophoresis utilized in transdermal drug delivery

A theoretical model of in vitro iontophoresis that utilizes radial mass transport is presented. The applicability of radial transport to the skin morphology of different species is determined by the density of low-resistance pores, which represents the density of skin appendages such as hair follicles or sweat glands. Radial transport is expected to dominate in the case where appendage density is low, in contrast to the linear transport mechanism that would dominate in the case of skin with high appendage density. Parameters such as the effective surface area of highly conductive pores and boundary-layer thickness are defined for the radial and linear transport limits and evaluated for the iontophoretic flux of pindolol hydrochloride through porcine skin. Based upon a decrease in the calculated boundary-layer thickness and an increase in drug flux with current density to a limiting value, it is concluded that radial mass transport is the dominant mechanism of iontophoretic transport under the experimental conditions described.