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 deri vative of capsaicin, the amount of SNA in the extracellular space was measu red. Transdermal iontophoresis is a process that enhances skin permeation o f ionized species by using an electric field as a driving force. Iontophore sis increased the amount of SNA in dialysate compared with passive diffusio n in this study. By using various polymers incorporated in formulations, in dicated hydrogels showed higher capacity for SNA delivery than solution for mulations. This result was possibly attributable to the antinucleant abilit y of polymers resulting in the increase of thermodynamic activity of SNA in formulations. Pretreatment with isopropyl myristate, a lipophilic penetrat ion enhancer, on rat skin enhanced transdermal delivery of SNA both for pas sive and iontophoretic penetration, indicating the possibility of reducing the surface area of the administrations site in clinical use. Microscopic e xamination revealed no or slight changes in the skin after iontophoretic tr eatment compared with penetration enhancer pretreatment. The histologic res ults also suggested iontophoretic treatment with 0.5 mA/cm(2) current densi ty of not more than 7-h application duration may be acceptable clinically. (C) 1999 Wiley-Liss, Inc.