Transdermal iontophoresis mechanisms

Pikal, M.J. 1990. Transport mechanisms in iontophoresis. I. A theoretical model for the effect of electroosmotic flow on flux enhancement in transdermal iontophoresis. Pharm Res 1 (2) 118. 

Hirvonen et al. [67] used dodecyl NA -dimethyl amino acetate (DDAA) and Azone as penetration enhancers in the transdermal iontophoresis of sotalol and salicylate. They compared the action of both enhancers in passive diffusion studies and iontophoretic studies and found no significant difference between the two, with the permeability of sotalol in the passive diffusion studies increasing to the order of magnitude found in the iontophoretic studies. The main mechanism of action of DDAA and Azone is the disordering of the lipids and the closing of iontophoretic penetration routes [123,124]. 

Iontophoresis by definition is the process of transport of ions into or through a tissue by the use of an applied potential difference across the tissue [52], Depending on the physicochemical characteristics of a molecular species, electrorepulsion is usually the primary mechanism of transdermal transport for ions, whereas electroosmosis and increased passive diffusion (as a result of the reduced barrier properties) are more prominent for neutral species [53]. In contrast, enhancement in flux for neutral or weakly charged species during electroporation arises predominantly from the reduced barrier properties of the membrane, whereas direct electrorepulsion is usually of secondary importance [25],... 

The present summary will cover only those technologies where the drug formulation itself is used to penetrate the skin via its mechanical energy. It will not describe any technology where a needle is used to puncture the skin, even if the needle is not visible to the patient or only the epidermis is punctured, such as mini-needles, microneedles, pen injectors, or autoinjectors. Also excluded are systems that ablate the skin mechanically or otherwise disrupt its chemical or mechanical structure to increase its permeability, such as laser ablation, microdermal ablation, electroporation, or iontophoresis. These are usually referred to as transdermal drug delivery, but can also be described as needle free. 

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