Electric field analysis on the improved skin concentration of benzoate by electroporation.

The objective in the present study was to understand the relationship between the increased skin concentration of benzoate as a model drug after topical application of its sodium salt and the electric field intensity produced in the skin barrier, the stratum corneum, by electroporation. A piece of excised abdominal hairless rat skin was set in a Franz type diffusion cell, and 0.5% sodium benzoate and physiological saline were applied to the stratum corneum and dermis sides, respectively. Two needle electrodes made of Ag were connected to an electrical power source, which produced exponentially decaying pulses. The electrodes were placed on the skin surface with a distance of 0.5 cm between both electrodes. After the 4 h passive permeation experiment, an electrical pulse was applied to the rat skin at 300 V every minute for 10 min. The skin was then removed from the diffusion cell, and the amounts of benzoate in different positions of the skin specimen were measured. Field intensity generated in the stratum corneum by electroporation was determined by a finite element method using a computer program. The amounts of benzoate at different sites in the skin were almost proportional to the mean field intensity in the corresponding stratum corneum. These results suggested that the enhancing effect of electroporation can be evaluated by the field intensity more directly than the application voltage.