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Research Reports |
FB Underwood, PT, PhD, ECS, is Professor of Physical Therapy, University of Evansville, 1800 Lincoln Ave, Evansville, IN 47722-0002
Address all correspondence to Dr Underwood at: fu2{at}evansville.edu
Iontophoresis of corticosteroids in the management of local inflammatory conditions is a controversial topic. The available evidence regarding the clinical efficacy of iontophoresis is contradictory and generally of low quality, with few notable exceptions. The research by Sylvestre and colleagues1 provides much-needed clarity to the technical aspects of this treatment and should serve as a stimulus to and basis for high-quality clinical trials.
In 1992, Petelenz et al2 determined in laboratory studies that dexamethasone is most effectively delivered via electromigration from the cathode of a direct current circuit. Despite their findings, many reference textbooks for electrotherapy used in professional (entry-level) physical therapist education programs persisted in listing dexamethasone as a positively charged ion. It is encouraging that most current textbooks (eg, Cameron,3 Prentice,4 Michlovitz and Nolan,5 Hayes and Nelson6) now clearly state that dexamethasone has a negative charge in solution and, therefore, should be delivered from the cathode. Despite this readily available information, some researchers fail to identify explicitly the electrode used to deliver dexamethasone. For example, Göko
lu et al7 compared iontophoresis with steroid injection for carpal tunnel syndrome and reported only that the active electrode had the same polarity as the dexamethasone. Their results indicated that injection was more effective than iontophoresis, but without knowledge of the methods used, these results cannot be considered strong evidence against iontophoresis. Other researchers, including Aygül et al,8 have continued to use the anode in an attempt to deliver dexamethasone. It is not surprising that these researchers failed to demonstrate a beneficial effect of iontophoresis for patients with carpal tunnel syndrome, given the reliance on electroosmosis to deliver the anti-inflammatory drug. Furthermore, given the results reported by Sylvestre et al and Petelenz et al,2 any researchers who have used the anode as the delivery electrode and who have reported clinical improvement and attributed the improvement to iontophoresis of dexamethasone must be challenged.
The key point of the research reported by Sylvestre et al is that the specific formulation of dexamethasone used for iontophoresis is crucial if the desired effect is to move the active drug across a barrier similar to human skin. As they noted in Table 1, using a preparation of dexamethasone without competing ions resulted in a nearly 6-fold higher flux of the drug than the next "best" commercially available solution. Nearly comparable flux rates were observed using the solution prepared with water, but it is not within the capability of most clinicians to prepare this formulation. Gurney et al9 recently reported that detectable amounts of dexamethasone were measured in samples of the semitendinosus tendon from only 7 of 16 subjects who were undergoing anterior cruciate ligament reconstruction. The median amount of dexamethasone recovered from the tendons was 6.1 ng·g–1 of tissue, which may be below the therapeutic threshold (which is unknown). However, Gurney et al used a formulation of dexamethasone that resulted in the third lowest flux of dexamethasone of the 8 formulations examined by Sylvestre et al. It may be that the competing ions (citrate) in the dexamethasone used by Gurney et al may have inhibited the movement of dexamethasone. Repeating the study by Gurney et al with a dexamethasone formulation without competing ions may be a worthwhile endeavor.
I have observed a wide variety of steroid preparations used by physical therapists who thought they were performing iontophoresis, as well as a wide variety of current types. Some of these clinicians have used over-the-counter corticosteroid creams, and others have attempted iontophoresis with pulsatile biphasic and pulsatile monophasic currents. Given the extreme variability in the clinical procedures used, it is little wonder that the results are variable as well. It is not uncommon that the assertion that an intervention "doesn't work for my patients" is the result of faulty application of the intervention by the therapist, not a faulty intervention. This is true for all interventions, not solely physical agents ("modalities"); manual therapy, motor learning, airway clearance, wound care, and other areas of practice all require attention to detail in order to be effective.
Another important finding reported by Sylvestre et al is the inverse relationship between the concentration of competing ions and the amount of dexamethasone moved across the barrier (Tab. 1). This also is likely relevant to iontophoresis of lidocaine from the anode. Sylvestre et al used a topical preparation, and clinicians often use injectable lidocaine for local anesthesia. Lidocaine intended for injection to achieve local anesthesia has a relatively high concentration of NaCl (generally 6 mg NaCl·mL–1 solution), meaning that a large quantity of sodium is likely moving in the electric field. Lidocaine intended for use to manage cardiac arrhythmias does not have added NaCl and may be better suited to iontophoresis to achieve local anesthesia. I agree absolutely with Sylvestre et al that there is no rational reason to mix lidocaine and dexamethasone during iontophoresis.
This research does not address the clinical question regarding the efficacy of iontophoresis, nor was that the intent of the research. Three clinical questions seem important to answer:
The implications of this research are clear. To reiterate, use the cathode as the delivery electrode, use a solution of dexamethasone with as few other anions as possible, and do not mix the dexamethasone with lidocaine. I am hopeful that the excellent research by Sylvestre and colleagues will stimulate clinical research and have a salutary effect on clinical practice.
 | References |
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lu F, Fndkolu G, Yorgancolu ZR, et al. Evaluation of iontophoresis and local corticosteroid injection in the treatment of carpal tunnel syndrome. Am J Phys Med Rehabil. 2005;84:92–96.[CrossRef][Web of Science][Medline]
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