Short-term iontophoretic and post-iontophoretic transport of model penetrants across excised human epidermis

The effect of short-term current application (0.4 mA for 10 min) on the epidermal transport of two model penetrants (butyl paraben, BP; caffeine, CF) of differing lipohilicity was investigated and compared to that produced by employing an established method of skin penetration enhancement (delipidisation). The aim was to investigate the mechanism of enhancement and route of skin permeation associated with each penetrant and mode of treatment. Franz cell diffusion experiments were conducted using human epidermal sheets and a saturated buffer solution (pH 7.4) of the respective penetrant, at a pseudo-finite dose. The effects of electrode type (anodal or cathodal) and current treatment protocol (iontophoresis or post-iontophoresis) on solute permeation was found not to be significantly different (p > 0.05). However, in contrast to BP, a significant increase in CF transport (3–5-fold) relative to untreated skin was observed when iontophoretic/post-iontophoretic treatment protocols were employed. The use of delipidised skin was found to enhance the permeation of both model penetrants to an extent greater than iontophoresis (BP: 3-fold; CF: 24-fold). Results from this study suggest that the permeation of the more hydrophilic CF across the skin, unlike BP, may involve multiple pathways. Electroperturbation of the epidermis was confirmed as the mechanism responsible for enhancing CF transport when electrical current was applied. Iontophoretic and post-iontophoretic enhancement may serve as a potential approach to enhance the topical delivery of CF in cosmetic or dermatological treatments (anti-cellulite, viral infections and psoriasis).