2003 Volume 63 Issue 1 Pages 20-28
The enhancing effect of switching iontophoresis on transdermal permeation in vitro was estimated as primarily being due to the enhancement of skin hydration. In this study, the effect of switching iontophoresis on transdermal absorption was investigated in vivo using sodium benzoate as a model drug. A couple of glass cells with Pt-electrodes were fixed on the abdominal skin of Wistar rats after hair removal. Four percent sodium benzoate solution was injected into each glass-cell and then the electric current at a constant voltage (5V, DC) was passed through the skin. Iontophoresis was carried out with switching at intervals of 5, 10 and 20 min or without switching. Switching iontophoresis at 10-min intervals showed significantly higher values than without switching. In switching iontophoresis, a rapid increase in the absorption rate was found immediately after switching. The drug absorption rate (%) in switching iontophoresis at 10-min intervals increased almost linearly, and it was clarified that 10-min intervals produced the maximal enhancing effect for transdermal absorption of sodium benzoate in this study. The current measured during iontophoresis increased transiently on switching. A high current value was observed at the time of switching, which was accompanied by the cancellation of skin polarization; thus the enhancing effect of switching iontophoresis on the transdermal absorption of sodium benzoate resulted from not only skin hydration, but also the cancellation of skin polarization.
