Iontophoresis
Introduction :
The introduction of substances into the body for therapeutic purposes by means of direct current
The substance is prepared in an ionic form and deposited subcutaneously according to the polarity of the ionic solution and of the electrode
It is a long established technique, with documented evidence of its use going back to the late 1700’s and early 1800’s
There are many clinical application depending on the particular ions utilised and the pathology in question
There are relatively few practitioners in the UK
[It is NOT the same as PHONOPHORESIS which involves driving ions across the skin with therapeutic ultrasound]
Physics :
A continuous direct (Galvanic) current needs to be employed
Some have advocated the use of pulsed galvanic or alternating currents, but with even less evidence to support their claims
It is assumed that the effects of the treatment are attributed to the delivered ions and not the direct current
Polarity
Works on the principle that likes repel and unlikes attract
Ions with a polarity which is the same as that of the stimulating electrode are repelled into the skin
Low current intensities appear to achieve favourable results
Usually applied with currents up to 5mA and with low ionic concentrations – up to 5%
Usually make the NEGATIVE electrode larger to avoid the skin irritation (whether the ionic driving electrode or not). Usually 2 x larger
Ionic Penetration
Usually considered to be less than 1mm
Any deeper penetration is considered to be due to local capillary circulation effects.
No evidence that the current itself is responsible for penetrations beyond this level.
The bulk of the ions that enter the tissues accumulate under the stimulating electrode
Can / may get recombination under this electrode
Ion Migration
The principle route or pathway through the skin appears to be via the sweat duct rather than through the epithelium itself
The stratum corneum, the hair folicles and sebaceous glands have high electrical impedance and allow the minimal passage of ions
Most iontophoresis solutions have a pH or 4.0 or more as this appears to facilitate the penetration of the ions through the epidermal layers
Acid/Alkaline Reactions
Will get ACID accumulation under the POSITIVE electrode (weak HYDROCHLORIC ACID)
Will get ALKALINE accumulation under the NEGATIVE electrode (SODIUM HYDROXIDE)
Will get a reactive hyperaemia under BOTH electrodes due to local vasodilation
The magnitude of the local reaction (independent of the ions utilised) will depend on :
Current Intensity (more current, greater reaction)
Time (longer time, stronger reaction)
Tissue Resistance (greater resistance, stronger reaction)
General Principles of Application
Preferably utilise a direct current stimulator
Constant current is preferable to constant voltage
Constant voltage stimulation can result in a burn more easily
The electrodes can be special pre gelled disposable electrodes or standard metal electrodes of various types
Some commercial iontophoresis electrodes have special wells or receptacle areas for the drug in question
The skin should be abrasion / cut free and the area carefully washed (soap & water is fine)
Some authorities have advocated the application of heat prior to the iontophoresis, but the experimental evidence does not support this. In fact, it appears to reduce the amount of drug passing through the epidermis.
Ensure that all electrode pads are thoroughly soaked in either tap water or other appropriate solution prior to application.
If pregelled electrods are being used, ensure that a good even contact is achieved.
Adequate fixation of the electrode and pad to the skin needs to be carefully maintained. Uneven current distribution can easily lead to skin burns and/or irritation
Explain to the patient what is expected and ensure that they know to report immediately if any untoward or painful sensations are felt.
Turn the current up slowly to the required amount
At the end of the treatment time, ensure that the current is turned down slowly.
References :
The most readable chapter on iontophoresis - MUCH more comprehensive than these brief notes - can be found in Belanger, A. Evidence Based Guide to Therapeutic Physical Agents, 2002. Philadelphia Lippincott Williams & Williams
In addition, I have several recent papers on iontophoresis that get mentioned in the Electrotherapy Newsletter should you want to chase up specific recent research materials - put iontophoresis into the search facility on the web pages and you will find them.
