Comparison of Depolarizing and Direct Current Systems on Iontophoretic Enhancement of Transport of Sodium Benzoate Through Human and Hairless Rat Skin

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Abstract
— A direct current (DC) system and a pulsed depolarization (PD) system were evaluated for their iontophoretic permeation of sodium benzoate, as a model drug, through hairless rat and human skin. Approximately the same initial permeation of sodium benzoate through the hairless rat skin was obtained at 0·1 mA for the DC device and at 3·0 mA for the PD device. Study of the drug's permeation was performed using a two‐chamber iontophoretic diffusion cell, over two cycles of three successive on‐off experimental conditions [stage I (off) 0–4 h, II (on) 4–6 h, III (off) 6–10 h, saline washing 10–24 h, IV (off) 24–28 h, V (on) 28–30 h and VI (off) 30–34 h]. Skin permeation rate during stage IV of the iontophoresis as compared with the control group through hairless rat or human skin for the DC system was 2–4 times that in stage I, whereas in the same stage using the PD system it was almost the same as in stage I. Impedance of skin decreased during the application of either system (stage II); however, the value significantly recovered during stage III only in the case of the PD system use on human skin. Histological observation revealed no tissue alteration in the hairless rat skin after using either system. When the DC or PD system was applied to volunteers, the minimum current density producing pain was 0·016 or 2·7 mA cm−2, respectively. These results suggested that the PD system was more appropriate for iontophoresis application than the DC system from the point of view of skin permeability of the drug and effect on the skin.