Transdermal iontophoresis of sodium nonivamide acetate II: Optimization and evaluation on solutions and gels

Sodium nonivamide acetate (SNA) is a newly designed derivative of capsaicin which reveals marked antinociceptive activity without producing an overt pungent sensation and skin irritation. The following iontophoretic drug delivery issues have been examined in this paper: (I) the competitive ion effect; (2) transdermal iontophoretic delivery from gel base; and (3) maximization of iontophoretic application mode from gel base. According to the theory of molal volume, divalent salt ions show higher buffering capacity on SNA iontophoretic transport than did monovalent salt ions. However, this effect also causes a great reduction of SNA transdermal flux. The experimental result of transdermal iontophoresis of gel indicated the flux of SNA decreased following the increase of viscosity. Using various polymers incorporated in gel formulations, indicated methyl cellulose and hydroxypropyl methyl cellulose showed higher capacity for SNA iontophoretic transport than the other materials. After a series of evaluation and optimization on the iontophoretic delivery of SNA, transdermal iontophoresis has provided a great capacity of enhancing SNA transport across the skin. The result of the present study is particularly helpful in the development of SNA transdermal delivery system and holds promise for the successful clinical development of an antinociceptive therapeutic regimen.