The Enhanced Iontophoretic Transport of TRH and Its Impedance Study

Abstract

The transdermal drug delivery of iontophoresis provides a noninvasive method for the administration of effective drugs. The enhanced iontophoretic transport of thyrotropin-releasing hormone (TRH), a tripeptide with molecular weight of 362 and a pK_a of 6.2, through an excised rabbit skin has been achieved by in vitro iontophoresis. The results indicate that the steady-state flux of TRH in a diffusion cell is proportional to the current density. In addition, the electrochemical properties of rabbit skin were studied with impedance spectroscopy, and it was found that the skin impedance decreased to a low and stable value with respect to its initial skin impedance while a current was applied through the rabbit skin. This is in good agreement with our experimental results on iontophoretic transport. As compared to passive diffusion, the iontophoresis dramatically increased the transport fluxes of TRH, and ethanol pretreatment further enhanced its iontophoretic transport. A practical implication of these results is that iontophoresis with a chemical permeation enhancer (ethanol pretreatment) can be applied to enhance and control the transdermal delivery of peptides.