Drug delivery systems, electrically active

As indicated in Fig. 1, a transdermal iontophoretic system requires that two electrode assemblies contact the patient s skin. The donor electrode (also known as the delivery or active electrode) contacts the drug reservoir. The counter electrode (also known as the return or receptor electrode) contacts the counter reservoir and completes the electrical circuit by providing a path for the current. The two reservoirs are separated from each other and contact skin over a fixed area. The electrodes apply an electric field across the skin by converting electric current supplied by the battery into ionic current moving in the skin and body. In doing so, a Faradaic reaction takes place at the electrode/ electrolyte interface. As described previously in this chapter, there is generally a linear dependence of the rate of drug delivery on this current. 

Transdermal delivery is suitable for small, generally lipophilic, potent molecules that require low input rates to achieve effective plasma concentrations. There may be a slow rate of increase of concentration if the drug forms a depot in the skin. Depot formation will also result in a slow decrease in concentration when the system is removed from the skin. These disadvantages can be overcome by the use of iontophoresis, by which the molecules are actively carried across the skin by a small electrical current. This provides a faster and more controllable transfer of drug. Intramuscular/Subcutaneous... 

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