Evaluation of transdermal iontophoresis of enoxacin from polymer formulations: in vitro skin permeation and in vivo microdialysis using Wistar rat as an animal model.

Polymers were used in vehicles to form hydrogel matrices in this study to evaluate the in vitro permeation and in vivo microdialysis of enoxacin. The highest transdermal delivery determined by area under flux-time curve (AUC) and intracutaneous enoxacin concentration were observed in methylcellulose (MC) and polyvinylpyrrolidone (PVP) hydrogels, respectively. To avoid the pH shift in vehicles during iontophoresis, buffer species were added to formulations to increase the buffer capacity. As expected, the permeability of enoxacin of anodal iontophoresis was larger than that of cathodal iontophoresis. Combination of benzalkonium chloride, a cationic surfactant as an enhancer, and iontophoresis exerted an enhancing effect for anionic enoxacin at pH 10.0. However, no effect or a negative effect was detected for cationic enoxacin in deionized water or pH 5.0 buffer, due to the shielding of the negative charge in the skin. The skin residue of enoxacin was slightly increased after the incorporation of Azone in PVP hydrogel. The result of in vivo microdialysis was in accordance with that of in vitro study. The effect of Azone on the intracutaneous enoxacin was more significant for in vivo microdialysis than in the in vitro study indicating the clinical feasibility of Azone for iontophoretic delivery. Microdialysis can be considered as a useful technique to investigate the pharmacokinetics of transdermal iontophoresis in vivo.