Since the FDA approved the first transdermal patch in 1981, the transdermal patch has grown into a two billion dollar market in the US with 35 approved products. Transdermal patches offer a variety of clinical benefits over other dosage forms. Because transdermal drug delivery offers controlled release of the drug into the patient, it enables a steady blood-level profile, resulting in reduced systemic side effects and often improved efficacy. In addition, because transdermal patches are user-friendly, convenient, painless, and offer multi-day dosing, it is generally accepted that they offer improved patient compliance.
The benefits of these conventional patches have been accompanied by problems and restrictions. The patches to date have been limited to a “one-size-fits-all” approach, so there is no way to control how much or when the drug is released. Also the size and type of drug molecule that will cross the skin barrier of its own accord are limited.
These limitations can be ameliorated through the use of iontophoresis, which is a method of propelling charged substance, normally medication or bioactive-agents, transdermally by electromotive force. A typical iontophoresis device consists of a power source, a computer processor, controller, drug reservoir and electrodes. This method involves the application of a low level of electric current directly to the skin, wherein the current is transferred from the electrode through the ionized drug solution as ionic flow. The electric current is used to control the amount and timing of drug delivery. Drug reservoirs may consist of a gel pad or membrane to which the drug solution is applied or injected. Today’s iontophoretic devices, due to their size and sophistication, require oversight by a trained medical professional, thus negating some of the possible benefits and cost savings of TDD.