Electroperturbation of the human skin barrier in vitro (I): the influence of current density on the thermal behaviour of skin impedance

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

The effect of short-term current application (0.4mA for 10min) 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).

Transdermal delivery of indomethacin by iontophoresis

The objective of this study was to construct a modified equation for the delivery of a drug by iontophoresis. Indomethacin was selected as a model since it has been widely used as a non-steroidal anti-inflammatory drug (NSAID) for external pharmaceutical preparations. The experiments were performed under a constant current in vivo using rat abdominal skin, and the plasma concentration was monitored by HPLC. Pharmacokinetic parameters were obtained from the plasma concentration profiles after intravenous injection. A theoretical value of the transdermal delivery of drug by iontophoresis was calculated from the plasma concentration and pharmacokinetic parameters. The experimental value was evidently higher than the theoretical one, suggesting the enhancement of passive diffusion with an increase of applied current. The modified equation was proposed for the delivery of a drug by iontophoresis incorporating enhanced passive diffusion.

Mechanistic studies of molecular transdermal transport due to skin electroporation

The application of electrical high voltage pulses has been shown to greatly enhance the transdermal transport of water-soluble compounds. The resistance of the skins most important barrier, the stratum corneum, drops within less than 1 µs by orders of magnitude. This effect is attributed to electroporation, a nonthermic phenomena known to occur in phospholipid double layers. The striking difference between the stratum corneum lipid layers and the usually investigated phospholipid systems is the phase transition temperature. While lipid layers used for electroporation experiments are in liquid crystal phase above the phase transition temperature, the stratum corneum lipids (phase transition at approximately 70 degrees C) form a rigid quasi-crystalline membrane at room temperature.After the electrical stimulus a recovery of the passive flux was found making high voltage pulsing a suitable tool for controlling transdermal drug delivery. By ordinary light microscopy no dramatic changes in skin structure were found supporting the thesis of electroporation. However the microstructure shows clearly persistent structural changes. Recently the involvement of Joule heating due to the electric stimulus was shown as an important factor for skin permeabilization and molecular transport.

Effects of iontophoresis and electroporation on the stratum corneum. Review of the biophysical studies

This review focuses on the effects induced by iontophoresis and electroporation on the stratum corneum of the skin. Hence, the aims were: (1) to contribute to the understanding of the mechanisms of drug transport by these methods; (2) to evaluate the safety issues associated with current application. Complementary biophysical methods were used to provide a complete picture of the stratum corneum. Even though the mechanism of drug transport is believed to be different, i.e., electrophoresis for iontophoresis and creation of new aqueous pathways for electroporation, the effects on the stratum corneum detected minutes after current application are very similar. For both methods, the major findings were: (1) a disorganisation of the lipid bilayers of the stratum corneum; (2) an increase in skin hydration; (3) a larger decrease in skin resistance induced by electroporation as compared to iontophoresis. These changes were partly reversible and depended on the amount of electrical charges transferred. The mechanisms of stratum corneum perturbations are discussed. These perturbations could explain partly the increase in drug transport. If iontophoresis is considered as a safe method of drug delivery, the data augurs for the safety of electroporation.