THE ENHANCED IONTOPHORETIC TRANSPORT OF TRH AND ITS IMPEDANCE STUDY

The transdermal drug delivery of iontophoresis provides a noninvasive method for the administration of effective drugs. The enhanced iontoph oretic transport of thyrotropin-releasing hormone (TRH), a tripeptide with molecular weight of 362 and a pK(a) of 6.2, through an excised ra bbit skin has been achieved by in vitro iontophoresis. The results ind icate that the steady-state flux of TRH in a diffusion cell is proport ional to the current density. In addition, the electrochemical propert ies of rabbit skin were studied with impedance spectroscopy, and it wa s found that the skin impedance decreased to a low and stable value wi th respect to its initial skin impedance while a current was applied t hrough the rabbit skin. This is in good agreement with our experimenta l 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 transpor t. 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.