Transdermal iontophoresis of sodium nonivamide acetate evaluated by in vivo microdialysis and histologic study

By using an intradermal microdialysis technique 22 h after the transdermal iontophoretic delivery of sodium nonivamide acetate (SNA), a synthetic derivative of capsaicin, the amount of SNA in the extracellular space was measured. Transdermal iontophoresis is a process that enhances skin permeation of ionized species by using an electric field as a driving force. Iontophoresis increased the amount of SNA in dialysate compared with passive diffusion in this study. By using various polymers incorporated in formulations, indicated hydrogels showed higher capacity for SNA delivery than solution formulations. This result was possibly attributable to the antinucleant ability of polymers resulting in the increase of thermodynamic activity of SNA in formulations. Pretreatment with isopropyl myristate, a lipophilic penetration enhancer, on rat skin enhanced transdermal delivery of SNA both for passive and iontophoretic penetration, indicating the possibility of reducing the surface area of the administrations site in clinical use. Microscopic examination revealed no or slight changes in the skin after iontophoretic treatment compared with penetration enhancer pretreatment. The histologic results also suggested iontophoretic treatment with 0.5 mA/cm² current density of not more than 7-h application duration may be acceptable clinically.