Iontophoresis is a physical process in which ions flow diffusively in a medium driven by an applied electric field. Iontophoresis is to be distinguished from the carriage of uncharged molecules by diffusive fluxes of other molecules, especially of solvent molecules, for example by electro-osmosis, that is to say by flux of uncharged solvent molecules carried as a cross-effect of iontophoresis. These phenomena, directly and indirectly, constitute active transport of matter due to an applied electric field. The transport is measured in units of chemical flux, commonly µmol/cm2h. The transport of a charged species of interest may also be measured in terms of a representative electric current, but that current might not be the whole of the current driven by the applied electric field.
Iontophoresis has purely laboratory experimental as well as therapeutic and diagnostic applications.
Iontophoresis is useful in laboratory experiments, especially in neuropharmacology. Transmitter molecules naturally pass signals between neurons. By microelectrophoretic techniques, including microiontophoresis, neurotransmitters and other chemical agents can be artificially administered very near living and naturally functioning neurons, the activity of which can be simultaneously recorded. This is used to elucidate their pharmacological properties and natural roles.
Therapeutically, electromotive drug administration (EMDA) delivers a medicine or other chemical through the skin. In a manner of speaking, it is an injection without a needle, and may be described as non-invasive. It is different from dermal patches, which do not rely on an electric field. It drives a charged substance, usually a medication or bioactive agent, transdermally by repulsive electromotive force, through the skin. A small electric current is applied to an iontophoretic chamber placed on the skin, containing a charged active agent and its solvent vehicle. Another chamber or a skin electrode carries the return current. One or two chambers are filled with a solution containing an active ingredient and its solvent vehicle. The positively charged chamber, called the anode, will repel a positively charged chemical species, whereas the negatively charged chamber, called the cathode, will repel a negatively charged species into the skin.
Common diagnoses treated with iontophoresis include plantar fasciitis, bursitis, lateral and medial epicondylitis (commonly referred to as tennis elbow and golfers elbow respectively) and some types of palmar-plantar hyperhidrosis.
Iontophoresis is commonly used by physical therapists and occupational therapists for the application of anti-inflammatory medications.
In the treatment of hyperhidrosis, tap water is often the chosen solution for mild and medium forms. In very serious cases of hyperhidrosis, a solution containing glycopyrronium bromide or glycopyrrolate, a cholinergic inhibitor, can be used.
Two iontophoretic patches have recently been approved for vaso-active therapeutic use by the FDA - Zecuity (2013) - containing the migraine drug sumatriptan - and Ionsys (2015), indicated for moderate-to-severe acute post-operative pain, delivering a therapeutic dose of the powerful opioid, fentanyl, on-demand. The entry of iontophoretic devices into the therapeutic mainstream will be followed with interest.
Iontophoresis of acetylcholine is used in research as a way to test the health of the endothelium by stimulating endothelium-dependent generation of nitric oxide and subsequent microvascular vasodilation. Acetylcholine is positively charged and is therefore placed in the anode chamber.
Reverse iontophoresis is a technique by which molecules are removed from within the body for detection. The negative charge of the skin at buffered pH causes it to be permselective to cations such as sodium and potassium ions, allowing iontophoresis which causes electroosmosis, solvent flow towards the anode. Electroosmosis then causes electrophoresis, by which neutral molecules, including glucose, are transported across the skin. This is currently being used in such devices as the GlucoWatch, which allows for blood glucose detection across skin layers.
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- Episode of TV series Quincy ME, featuring the use of iontophoresis to commit a murder
- Iontophoresis Protocols for use in Physical Therapy and Sports Medicine
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