PT Classroom - Penetration of Iontophoresis Versus Phonophoresis in Human Muscle Tissue – A Literature Review  ׀ by Jennifer Hill, MPT, CSCS


Many drugs are poorly absorbed through skin by passive diffusion alone. The use of topical agents often requires vehicle formation or chemical penetration enhancers that are potential irritants or sensitizers (1). Iontophoresis and phonophoresis are methods of driving topically applied substances across tissues by utilization of electric current or ultrasound, respectively. These physical modalities offer methods for enhancing the percutaneous absorption of selected drugs (2).


Iontophoresis is the use of electromotive force to enhance percutaneous absorption of a drug or chemical. Iontophoresis usually employs a direct current between 0.5 and 5.0mA2. The use of iontophoresis has fluctuated over the years, partly due to concerns about chemical burns of the skin that can accompany iontophoresis treatment and the need for additional research demonstrating the efficacy of the technique (3).

Many studies have been conducted on the topic of iontophoresis; however, few have succeeded in accurately quantifying the useful data and than applying the statistics to the clinical setting. For example, Costello et al. (3) provided general information pertaining to iontophoresis including: advantages/disadvantages, influencing factors, applications and history. It was a thorough review of previous research which demonstrated the need for further research. However, his research would have better validity if he used statistical analysis to support his conclusions. Therefore, the more quantitative analysis rather than the qualitative analysis would provide more meaningful information. Costello et al. (3) concluded that the use of iontophoresis in medicine is likely to increase, but questioned the extent to which physical therapists will be involved in this expansion of usage. This secondary reference provides a good foundation for researching the subject of iontophoresis as well as produces results that are supported and generalizable.

The technical characteristics and mechanisms of action of iontophoresis can be used as sources of research for the future. Why does iontophoresis work the way it does and what would happen if any conditions were changed? Kassan et al (2) reviewed the underlying principles, current status, and potential of iontophoresis. Previous research is adequately reviewed; however the lack of standardized experimental conditions with respect to intensity of current, frequency, waveform, on/off ratio of current, tissue pH and failure to use adequate controls made it difficult to assess many of the previous studies. The lack of gold standards in the use of iontophoresis and the numerous varying methods and measurement techniques made it difficult to compare/contrast research findings.

Lack of control has a large effect on the conclusion of findings (2). Selection of homogenous groups was rarely performed in any studies reviewed by Kassan. The subjects had different types of injuries, damages to varying tissues, and reported various levels of pain prior to onset of study. The level of control increased in terms of treatment application. Each study had clear specifications for how to the treatment was to be administered (4-6). Of course, each research design differs slightly, but parallels can be drawn and general conclusions can be made despite such differences.

Various levels of measurement can also make it difficult to compare/contrast results from different studies. Ordinal data is most often collected by means of some type of self perceived pain scale (3-6). This indirect measurement scale always produces some level of threat to validity, since each individual perceives pain differently and levels of pain tolerance vary from person to person. Therefore, the researcher must take these threats into consideration when critiquing his/her methods, findings, and conclusions.

Phonophoresis refers to a specific type of ultrasound application in which pharmacological agents such as corticosteroids, local anesthetics and salicylates are introduced (7). Ultrasound is primarily used for its ability to deliver heat to deep musculoskeletal tissues such as tendon, muscle, and joint structures. The depth of penetration is roughly inversed related to the frequency (8). The therapeutic effects of heat likely involve increased regional blood flow, increased soft tissue extensibility, and decrease pain and muscle spasm (8). The mechanical properties of ultrasound are less well defined but are believed to alter cellular permeability and metabolism (9). The tissue response to these non-thermal effects may be important in the promotion of wound healing (9).

Due to their close relationship in methodology, phonophoresis and ultrasound are often compared in terms of effectiveness. Klaiman et al (7) looked at the differences in pain response after the previously mentioned treatments. Therefore, a threat to internal validity was present in spontaneous healing. The effects of no treatment were not taken into comparison; therefore, previous literature was relied upon to provide evidence in support of treatment over no treatment.

Klaiman et al. (7) conducted a thorough literature review and pointed out that the efficacy of phonophoresis has not been conclusively established. In looking at both ratio and ordinal data, these studies have a number of methodological shortcomings, including inadequate blinding, lack of randomization, and questionable assessment of pain relief (7). Nonhomogeneity of subjects was a concern for control, but all of the testing procedures were adequately controlled. No differences were found between the phonophoresis group and the ultrasound group in measurements of pain (visual analog system) or tolerance to application of a pressure algometer.

From the review, one can make the case for the need for controlled clinical studies comparing the efficacy of iontophoresis and phonophoresis. This need is clearly shown by the lack of total research conducted on the topic as well as the lack of measured physiological changes associated with each modality. Research questions that need to be answered relate to the actual depth of drug penetration, the appropriate concentration of drug, the type of vehicle preparation (cream, gel or ointment), the ultrasound frequency, and the ultrasound mode (continuous or pulsed) (7).

In the research available that does compare/contrast iontophoresis and phonophoresis, the lack of quantification seems to be evident. Most measurements are done in relation to pain reduction, rather than depths of muscle/tissue penetration. Conclusions that suggest that iontophoresis and phonophoresis are promising methods of enhancing topical delivery of both dermatological and non-dermatological drugs (2) are clinically applicable and important but further research should be conducted to search for more statistical, physiological evidence. It has indeed been proven through numerous research findings that both iontophoresis and phonophoresis are effective methods of treating musculoskeletal disorders. However, a future study should be designed to quantify the actual differences of these treatments by using them in ways that simulate realistic clinical situations.


Last revised: March 8, 2009
by Jennifer Hill, MPT, CSCS


1) Ronade VV. Drug delivery systems: transdermal drug delivery. J Clin Pharmacol. 1991;31:401-18.
2) Kassan DG, Lynch AM, et al. Physical enhancement of dermatological drug delivery: Iontophoresis and phonophoresis. J AM Acad Derm. 1996;34:657-66.
3) Costello CT, Jeske AH. Iontophoresis: Applications in transdermal medication delivery. Phys Ther. 1995;75:554-563.
4) Maloney M, Bezzant JL, et al. Iontophoresis administration of lidocaine anesthesia in office practice. J Dermatol Surg Oncol. 1992;18:937-40.
5) Russo J, Lipman A, et al. Lidocaine anesthesia: comparison of iontophoresis, injection, and swabbing. Am J Hosp Pharm. 1980;37:843-7.
6) Kennard CD, Whitaker DC. Iontophoresis of lidocaine for anesthesia during pulsed dye laser treatment of port-wine stains. J Dermatol Surg Oncol. 1992;18:287-94.
7) Klaiman MD, Shrader JA, et al. Phonophoresis versus ultrasound in the treatment of musculoskeletal conditions. Med Sci Sports Exerc. 1998;30:1349-1355.
8) Lehman JF, DeLateur BJ, et al. Heating of joint structures by ultrasound. Arch Phys Med Rehabil. 1968;49:28-30.
9) Dyson M, Pond JB. The effect of pulsed ultrasound on tissue regeneration. Physiotherapy. 1970;56:136.

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