IONTOPHORESIS

The term Iontophoresis is simply defined as ion transfer( ionto=ion; phoresis=transfer). iontophoresis, also called electromotive drug administration(EMDA), is a technique which uses an electric current to deliver a medicine or other chemical through the skin. it is sometimes called ” an injection without the needle”.

The use of iontophoresis was first reported in the early 1900s. historical uses of iontophoresis include use of tap water or an aluminum compound to treat hyperhidrosis of hand or feet. iontophoresis has been used to accelerate wound healing using iodine, zinc or copper  compounds(solan and soltani, 1986).

It is a non-invasive, specialized technique of electrical stimulation that uses eletrical polarity of continuous direct current to ionize medicines placed beneath surface electrodes and transfer them into the body through the skin.

Route of ion transfer

The primary route of ion transport across the skin is thought to be through the skin pores and the hair follicles. however more recent studies suggest that, iontophoresis may promote transdermal drug penetration, primarily by increasing the permeability of the stratum corneum, the main barrier to transdermal drug uptake.

MECHANISM OF IONTOPHORESIS( BASIC PRINCIPLE OF IONTOPHORESIS):

 

  • In order to ‘drive’ the ions into the tissues, a direct (galvanic) current needs to be employed.
  • The technique is completely non-invasive, and the ion concentration required is very low.
  • Essentially, the substance to be driven into the tissue needs to be ionic in nature, and must be placed under the electrode with the same charge. it can be made to move in either direction depending upon the polarity applied.
  • When the solution of the wet pad or sponge that contains the drug is applied over the skin and a constant direct current is passed, electrolysis of the chemical produces the ions, positively charged ion and negatively charged ion.

The positively charged chamber, called the anode, will repel a positively charged chemical into the skin.

The negatively charged chamber, called the cathode, will repel a negatively charged chemical into the skin.

 

PHYSICS OF IONTOPHORESIS:

The following physical considerations need to be done while following iontophoresis:

⇒The amount of substance introduced;

  • The basic formula for using iontophoresis to know the amount of substance introduced in grams is- I×T×ECE.
  • Where I, is intensity of current in amperes. T, is the time in hours.  ECE, electrochemical equivalance of the substance.
  • The number of ion entering the tissues from any given area of active electrolyte is proportional to both the current density and the time of application.

⇒Ionic polarity;

  • The basis of successful ion transfer lies in the physical principle: like poles repel and unlike poles attract.
  • The ions being charged particles with positive or negative valences are repelled into the skin by identical charge on the electrode surface placed over it.

⇒Low level amperage;

  • The lower the intensity of current, greater is the amount of penetration of the ions through the skin.
  • The current is usually applied with currents up to 5mA.
  • With low ionic concentration, up to 5%
  • Treatment time typically in the 10 to 30 minute range

<

p class=”green h3″>ELECTRODES:

The electrode under which the ionic solution is placed is called the ACTIVE electrode (other terms include TREATMENT electrode or DELIVERY electrode). The other electrode, which is used to complete the circuit is most commonly called the DISPERSIVE, INDIFFERENT, INACTIVE or RETURN electrode.

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.

Iontophoresis electrode system Iontophoresis electrode system
Iontophoresis electrode system Iontophoresis electrode system
Examples of commercialliy available iontophoresis electrode systems

 

 

 

 

 

 

It is not necessary to use these (commercial) electrodes, and for many years, therapists have used various metal / foil electrodes with the substance needed for the treatment applied to the wet/damp gauze between the metal electrode and the skin surface.

It has been suggested that commonly, the NEGATIVE electrode is made larger (relative to the positive electrode) to avoid skin irritation (whether the ionic driving electrode or not). Figures often cited suggest that the negative (cathode) electrode should be 2 x larger than the positive (anode) electrode.

Anodal and Cathodal Reactions in response to Iontophoresis

Cathode Anode
NEGATIVE electrode POSITIVE electrode
Attraction of +ve ions Attraction of -ve ions
Alkaline reaction by the formation of NaOH Acid reaction by the formation of HCl
Increased density of proteins Decreased density of proteins
Increased nerve excitability via a depolarisation effect Decreased nerve excitability via a hyperpolarisation effect (sometimes called anode blockade)

 

PHYSIOLOGICAL EFFECT OF IONTOPHORESIS

Physiological effects of iontophoresis depend on the ion(drug) selected for treatment, since each ion is different. specific ion are utilized for the treatment of specific condition and some of the effects common to all are:

1)Ion penetration:

  • Penetration is generally less than 1 mm, with subsequent absorption to deeper tissues via capillary circulation and transmembrane transport.
  • The depth of drug delivery with iontophoresis is 3mm to 20 mm.
  • The bulk of the ion deposited are found directly at the site of the active electrode.

2)Acid/Alkaline reaction:

  • The anode(+) produces an acid reaction, a weak hydrochloric acid, where as the cathode(-) produces a strong alkaline reaction, sodium hydroxide.
  • The anode is sclerotic and tends harden tisues, serving as an analgesic, possible due to the local release of oxygen, aiding in the vitality of tissues.
  • the cathode, conversely is sclerolytic, a softening agent, releasing hydrogen and is utilized clinically, in the management of scars, burns and keloids.

3)Hyperemia:

  • the anode and cathode both produce hyperemia due to vasodilatation as a result of heat production in accordance with joule’s law.
  • In most instances, the reddening of skin under both electrodes disappear within 1 hour of the treatment.

4)Dissociation:

  • Normally ionizable substances dissociate in solution releasing ions and radicals free to drift towards the opposite poles, when a direct current is passed.

<

p class=”green h3″>THERAPEUTIC EFFECT:

The therapeutic effects of iontophoresis depend upon the nature of the drug introduced into the  tissues. the substance used in different purposes are listed in table in indication and uses of iontophoresis.

INDICATION AND USES OF IONTOPHORESIS:

Drug / Solution Main Indication(s) Rationale Parameters

Acetic Acid

Calcific tendinitis (myositis ossificans)

Acetate believed to increase solubility of calcium deposits in tendons (and other soft tissues)

2 – 5% aqueous solution
NEGATIVE pole

Calcium chloride

Muscle spasm (also hypersensitive peripheral nerves)

Calcium thought to stabilise excitable membranes, appears to decrease excitability threshold in peripheral nerves and skeletal muscle

2 – 5% aqueous solution
NEGATIVE pole

Dexamethasone

Inflammation

(synthetic) anti inflammatory

4mg/mL aqueous solution
NEGATIVE pole

Hydrocortisone

Inflammation

Steroid based anti inflammatory

0.5% ointment POSITIVE pole (Rothstein et al)

Hydrocortisone, prednisone

Inflammation

Steroid based anti inflammatory

NEGATIVE pole (Belanger)

Iodine

Adhesive capsulitis
Other soft tissue adhesive presentations
Infection (microbial)

Iodine acts as a broad spectrum antibiotic. Its actions in relation to adhesive presentations appear not to be fully understood

5 – 10% solution (some use ointment)
NEGATIVE pole

Lidocaine

Soft tissue pain
Inflammation

Local anaesthetic effects (blocks peripheral nerve activity).
May stimulate healing

4 – 5% solution (ointment)
POSITIVE pole

Magnesium sulphate (sulfate)

Muscle spasm
Myositis

Thought that ‘relaxing’ effect is achieved by decreased excitability of muscle membrane and reduced activity at neuromuscular junction

2% aqueous solution (ointment)
POSITIVE pole

Hyaluronidase

Oedema (local)
Subacute and Chronic stages

Increases permeability in connective tissues thus allowing dispersion of accumulated fluid. Hydrolysation of hyaluronic acid

Delivered after reconstitution with 0.9% sodium chloride (Normasol) to give a 150µg/mL solution
POSITIVE pole

Salicylates

Muscle and Joint pain
Acute and Chronic

Mode of action akin to Asprin – analgesia and anti inflammatory. Inhibits synthesis of prostaglandins

2-3% sodium sallicylate solution
OR
10% trolamine sallicylate ointment
NEGATIVE pole

Tolazoline hydrochloride

Ulcers (open wounds)

Stimulates local blood flow
Stimulates tissue healing (thought to be via inhibition of local vascular smooth muscle contraction)

2% aqueous solution
POSITIVE pole

Zinc Oxide

Open wounds – ulcers
Some dermatological conditions

Antiseptic effects related to the zinc.
May stimulate healing

20% ointment
POSITIVE pole

Tap Water

Hyperhydrosis
(illustrations below)

Suppresses sweating in palms, soles of feet, axilla through ?keratin plug formation in ducts

Equal time with POSITIVE and NEGATIVE polarity – use 2 x hand baths. Reverse polarity 1/2 way through treatment (typically 30 minutes : 15+15)

APPLICATION OF IONTOPHORESIS:

  • The skin should be abrasion / cut free
  • The area carefully washed(soap and water is fine)
  • Dry electrodes are inappropriate and should not be used
  • If pregelled electrodes 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.
  • The drug to be applied is placed under the correct electrode, i.e. if the drug is having a negative charge( iodine), it should be applied under the negative electrode for reason describe earlier.
  • The positively charge ion must be applied under the positive electrode.
  • Uneven current distribution can easily lead to skin burns and irritation
  • Explain to the patient what is expected and ensure that they knowto report immediately if any painful sensation are felt.
  • Turn the current up slowely to the required amount
  • At the end of the treatment time, ensure that the current is turned down slowly.

DOSAGE OF IONTOPHORESIS:

  • It is found that, when the time of treatment is increased for a given current density, the transfer of ions is proportionally smaller.
  • The current densities that are tolerable comfortably is in the region of 0.1- 0.2mA/cm².
  • However, the recommended maximum safe current density under the cathode is 0.5mA/cm², and for the anode 1.0mA/cm²
  • Thus, the dosage can be expressed in ‘mA min’ i.e. the total current multiplied by the treatment time.
  • With children the initial dose should be even less between 50-70 mA min.
  • In term of the intensity of current applied, it is suggested to limit the total current to 5-20mA and the duration of treatment to 10- 30 minutes.

CONTRAINDICATION:

  • Cardiac pacemaker or arrhythmia
  • Unconscious patient
  • Recent radiotherapy
  • Carotid sinus
  • Area of venous and arterial thrombosis and thrombophlebitis
  • Pregnancy
  • Early tendon transfer/ repair( electrical stimulation is contraindicated in the early tendon repair/ transfer, before the completion of 5th week , as the strong muscle contraction might cause a muscle or tendon damage.
  • Malignancy
  • Infected wound and skin lesions
  • Hemorrhage

DANGERS:

  1. Burn
  2. Electric shock
  3. Skin irritation
  4. Systemic effect: just like nausea, headache, abdominal pain or mild dryness of the mouth. the patient should be warned to avoid vigorous exercise immediately after treatment and if the symptoms are severe the area of treatment should be reduced.

IONTOPHORESIS VS PHONOPHORESIS

  • Iontophoresis uses electrical current to transport ions into tissues
  • Phonophoresis uses acoustic energy (ultrasound) to drive molecules into tissue.
%d bloggers like this: