Role of conductivity in iontophoresis. 2. Anodal iontophoretic transport of phenylethylamine and sodium across excised human skin.

The anodal iontophoretic transdermal delivery of a model cation, phenylethylamine (PEA), across excised human skin was investigated to define the role of conductivity in iontophoresis. The ratio of the specific conductance of PEA in deionized-distilled water to that of the solution applied in the donor compartment (buffer+PEA) was employed to assess the relationship between the flux of PEA and the conductivity. The flux of PEA was linearly related to the ratio of specific conductance at 5 and 20 mM PEA for a variety of experimental conditions. A curvilinear relationship was observed at 1 mM PEA concentration, particularly when the conductivity of the donor solution was low. It is therefore hypothesized that a threshold conductivity in solution exists above which a linear relationship between iontophoretic flux and specific conductance is observed. The present study confirms that conductivity of an ion in a solution provides a simple means of estimating the competitive transport between solute and other ions during transdermal iontophoresis.