Electric Delivery

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December 2004

By Delmas Bolin, MD, PhD, FACSM, and Michael Goforth, MS, ATC

When hip-hop music impresario P. Diddy was suffering from chronic knee pain the night before his well-publicized New York City Marathon run, he was treated with iontophoresis for his pain. After completing the marathon, the rap star had no knee pain and credited iontophoresis for his ability to run the race.¹

Since P. Diddy's endorsement, the role of iontophoresis in the management of chronic overuse conditions has received increased attention. When famous stars or athletes embrace a treatment, many patients quickly research it via the Internet and, armed with this knowledge, seek a physician or therapist in search of the miracle cure. Patients view iontophoresis as a "secret" pain treatment that can speed recovery from weekend warrior overuse injuries. As with any treatment, the physical therapist and treating physician should understand when to use iontophoresis and exactly what benefits it can and cannot achieve for the patient.

Iontophoresis is a method of local transdermal drug delivery, which uses direct electric current to "drive" charged molecules through the skin and into the subcutaneous tissues. Iontophoresis has been used with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, local anesthetics, and salicylates to produce analgesia in a variety of clinical settings. Although the exact mechanism of drug delivery is unknown, it is thought that charged molecules of the treatment solution follow the electric current stream into the subcutaneous tissues through skin pores and hair follicles. Iontophoresis has been demonstrated to "drive" dexamethasone to a tissue depth of 5 to 20 mm. The tissue concentration decreases exponentially with depth and is dependent on treatment location as well as the treatment molecule charge and size, eg, hip or knee.² In addition to medicinal effects, electric current increases local blood flow for up to 1 hour and produces mild skin erythema after treatment.³ Pain relief is usually reported the same day but may take two to three treatments and up to 48 hours before significant relief is noted.

Figure 1A. When administering iontophoresis treatments, uniform and good skin contact is essential. A current generator unit is then attached to the membrane electrode and treatment commences.

Iontophoresis requires very little technical skill. Usually, the treatment solution is placed on a semipermeable, adhesive membrane and tightly adhered to the skin. Uniform, good skin contact is essential. A current generator unit is then attached to the membrane electrode and treatment commences (Figure 1A). Current varies by the surface area of the membrane and is typically 0.1 to 0.5 mA/cm². The current is set to a level where the patient experiences a therapeutic sense of tingling.

Newer self-contained patch electrodes do not require an external battery-driven unit and are therefore more portable. Twelve-hour (40 mA/min) and 24-hour patch systems (typically 40-80 mA/min) use a dual chamber electrode system (Figures 1B and 1C). The patch membrane contains embedded zinc and silver chloride electrodes. The battery is activated when the treatment solution bathing one electrode comes into contact with the saline solution that bathes the opposite electrode, creating the necessary charge to drive molecules into the desired tissues.

Figure 1B and 1C. Newer self-contained patch electrodes do not require an external battery-driven unit, and are more portable. Twelve-hour (40mA/min) and 24-hour patch systems (typically 40-80 mA/min) use a dual chamber electrode system. The patch membrane contains embedded zinc and silver chloride electrodes, and is activated when the treatment solution bathing one electrode comes into contact with the saline solution which bathes the opposite electrode, creating the necessary charge to drive molecules into the desired tissues.

BARRIERS TO USE
For professional therapists, there are financial considerations that may limit use. Reimbursement is comparable to that for other electrical modalities. Fortunately, the equipment for iontophoresis is relatively inexpensive. Some vendors will negotiate to provide a complimentary unit with the purchase of a specified number of electrodes. It is important to track your payor reimbursement. There is at least one major-market insurance carrier that will not reimburse for iontophoresis at all, and a few that reimburse at discounted levels.

Most states require a separate physician's prescription for iontophoresis by an athletic trainer or physical therapist. Many of the medicines that are used are controlled substances, and some, such as diclofenac, may require a compounding pharmacist to have them in appropriate solution for iontophoresis. Physician experience and training with iontophoresis are extremely variable. Consequently, physicians may view iontophoresis as a money-maker for physical therapists. This is particularly true in areas of the country where the payor mix is highly capitated, placing the physician at financial risk for the patient's expense during physical therapy. With these market stressors in place, physician referrals tend to be directed to lower-cost, fewer-procedure physical therapists. In this setting, physical therapists requesting a prescription are often refused and many abandon efforts to obtain an iontophoresis prescription.

REASONS FOR USE
Several uses have been proposed for iontophoresis, and reports have examined its effectiveness for anesthesia prior to dermal procedures, treatment of hyperhydrosis of the hands and feet, and treatment of acute and chronic overuse injuries.⁴

At Virginia Tech, we primarily see acute and overuse injuries. We use iontophoresis for analgesia in players in conjunction with rehabilitation as a safe and pain-free alternative to injection. As a practical matter, we find iontophoresis most helpful with superficial acute injuries, including muscle and tendon strains, contusions, and ligament sprains (Table 1). We also see improved pain and better rehabilitation with iontophoresis in superficial subacute injuries. Examples include lateral epicondylitis, plantar fasciitis, peroneal tendinitis, DeQuervain's tenosynovitis, and iliotibial band syndrome. Iontophoresis provides improved analgesia in conjunction with systemic NSAIDs to promote rehabilitation in the early stages of treatment for these conditions. Generally, we use the self-contained patch electrode with 4 mg dexamethasone in the negative electrode at a dose of 40 to 80 mA/min. We have also used 2% acetic acid in distilled water in the negative electrode at a dose of 80mA/min to help in quadriceps contusions at risk for myositis ossificans. A typical schedule is six treatments in duration, usually on an every-other-day basis.

The decision to add iontophoresis to a rehabilitation protocol should be based on the best available evidence. Patients' expectations should be guided by scientific investigation rather than anecdotal report or personal experience. Unfortunately, there are very few well-controlled randomized studies of the effectiveness of iontophoresis. The effect of iontophoresis using the NSAID diclofenac versus sodium salicylate has been studied in lateral epicondylitis. Both treatments decreased pain, but diclofenac-treated patients had less pain with palpation and resisted wrist extension.⁵ Iontophoresis of 0.4% dexamethasone also produced significant improvements in lateral epicondylitis pain after only 2 days, but there was no significant difference at 1 month.⁶ A second placebo-controlled, double-blind study of dexamethasone in lateral epicondylitis treatments found no effect greater than placebo at the 3- and 6-month follow-up.⁷

A double-blind, placebo-controlled study of plantar fasciitis used iontophoresis of 0.4% dexamethasone added to traditional treatments. Over 2 weeks (six treatments), the dexamethasone group had significantly lowered pain scores. No difference was seen between the groups at the 1-month follow-up.⁸

The evidence does not demonstrate that iontophoresis improves muscle function or long-term result for common overuse injuries. Nonetheless, iontophoresis appears to increase analgesia in the initial treatment (1-2 weeks) of many common overuse injuries. Pain relief may facilitate early rehabilitation and, while not improving outcome, may permit the patient and athlete to maintain cardiovascular fitness while healing.

CLINICAL ADVANTAGES
Iontophoresis is helpful because it can help avoid systemic administration of medication. First-pass metabolism by the liver significantly reduces oral medication concentrations. Local delivery systems avoid first-pass metabolism. Although the concentration of medicine at a given site is unknown, iontophoresis can produce pain relief without the need for bolus injections of medications. Further, complications seen with steroid injection, such as fat pad atrophy, skin atrophy, and tendon rupture, have not been reported with iontophoretically delivered cortico steroids.

A (SMALL) WORD OF WARNING
Iontophoresis is very well tolerated by most patients. There are a few contraindications for use: a previous adverse reaction or hypersensitivity to electrical stimulation, patient sensitivity to the administered medication, and if the underlying diagnosis has not been established. The most common problems encountered are skin irritation and burns. Excessive amperage can lead to thermal injury. The amperage should be immediately reduced if the patient reports any sensation other than mild tingling. Skin irritation can result from current-generated hydrogen and hydroxide ions.

The treatment site should be properly prepared. Cleanse the skin with alcohol. The areas where the electrodes are to be placed should be free of trauma and excess body hair. Shaving can cause nicks in the skin and so clipping excess hair is recommended. Care should be taken with electrode placement. The optimal placement is for the treatment electrode to be placed directly over the area to be treated. The electrodes should be tightly adherent to the skin. Loose electrodes contribute to thermal burns and irritation. The patient should be advised not to extend or flex the area being treated or to press on or lean against the electrodes during treatment. Secure the patch electrodes (see Figure 1C), but never bind or tape them in place. The return electrode should be carefully placed also. For example, in treating plantar fasciitis, a position over the plantar forefoot would be better than over the thickened skin and fat pad of the heel. To maximize current delivery and avoid contamination, electrodes should never be reused.

Although it does not improve long-term results, iontophoresis can be particularly helpful in controlling pain in the early treatment of acute and chronic overuse conditions. Properly administered, it can prevent some of the complications encountered with oral medications and facilitate earlier, more aggressive rehabilitation. Newer self-contained patches are easy to use and relatively cost-effective. It is well tolerated with few side effects and may be a useful addition to your "bag of tricks" with appropriate patients.

Delmas Bolin, MD, PhD, FACSM, is an associate professor, sports and family medicine, at the Edward Via Virginia College of Osteopathic Medicine and is associate team physician for Virginia Tech Athletics, Virginia Polytechnic Institute and State University, Blacksburg, Va; Michael Goforth, MS, ATC, is director of athletic training, Virginia Tech Athletics, Virginia Polytechnic Institute and State University.

REFERENCES

Parker-Pope T. P. Diddy's secret: athletes' treatment for pain can help weekend warriors. Wall Street Journal. November 11, 2003:D1.
Glass J, Stephen R, Jacobson S. The quantity and distribution of radiolabeled dexamethasone delivered to tissue by iontophoresis. Int J Dermatol. 1980;19:519-525.
Evans TA, Kunkle JR, Zinz KM, Walter JL, Denegar CR. The immediate effects of lidocaine iontophoresis on trigger-point pain. J Sport Rehabil. 2001;10:287-8.
Starkey C, ed. Therapeutic Modalities. 3rd ed. Philadelphia: FA Davis Co; 2004.
Demirtas RN, Oner C. The treatment of lateral epicondylitis by iontophoresis of sodium salicylate and sodium diclofenac. Clin Rehabil. 1998;12:23-29.
Nirschl RP, Rodin DM, Ochiai DH, Maartmann-Moe C. Iontophoretic administration of dexamethasone sodium phosphate for acute epicondylitis. A randomized, double-blinded, placebo-controlled study. Am J Sports Med. 2003;31:189-195.
Runeson L, Haker E. Iontophoresis with cortisone in the treatment of lateral epicondylitis (tennis elbow) - a double-blind study. Scand J Med Sci Sports. 2002;12:136-142.
Gudeman SD, Eisele SA, Heidt RS, Colosimo AJ, Stroupe AL. Treatment of plantar fasciitis by iontophoresis of 0.4% dexamethasone: a randomized, double-blind, placebo-controlled study. Am J Sports Med. 1995;25:312-316.

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December 2004