Applicability of switching iontophoresis with special reference to its influence on rat skin

The effects of switching iontophoresis, including the difference in donor solution on rat skin, were investigated regarding the pH alteration in a donor chamber, skin and plasma concentrations, microphotography and histopathological scoring. Although the pH of donor solution was presumed to be changed in case that platinum was used as an electrode, a pH alteration was hardly observed in switching iontophoresis that used buffer solutions as a donor solution. In contrast, the pH alteration was observed in non-switching iontophoresis. The relation between the plasma and skin concentrations depended on the solvent used. The choice of solvent used was important because the effect of switching iontophoresis on skin permeability and skin damage depended on the solvent. Moreover, when the drug solution was used as a donor, skin damage was alleviated as the switching interval became shorter. Skin damage was low when the agar gel containing the drug was used as a donor in comparison with the drug solution, exception made of 5 and 10 min interval switching. Polarity switching was suggested to bring about not only cancellation of skin polarization but also the suppression of pH alteration in the donor chamber. Therefore, switching iontophoresis was more effective for transdermal administration with lower skin damage compared with the non-switching type.