The use of ultrasound as an enhancer for transcutaneous drug delivery: phonophoresis.

Phonophoresis is the use of ultrasound (US) to enhance the delivery of topically applied drugs. The purposes of this article are (1) to review the basic principles of transcutaneous drug delivery, (2) to summarize the functional anatomy of the skin pertinent to phonophoresis, (3) to outline the physiological principles of US as an enhancer of topically applied drugs, (4) to review the literature on the efficacy of phonophoresis, (5) to discuss the relevance of US as an enhancer of topical drugs in the practice of physical therapy, and (6) to outline areas of needed research. Seventy-five percent of the studies reviewed reported positive effects of US on local subcutaneous drug diffusion, but some systemic effects were reported. This research review indicates that to maximize the clinical effectiveness of phonophoresis: (1) the topical drug (both the drug and the carrying agent) should transmit US; (2) the skin should be pretreated with US, heating, moistening, or shaving; (3) the patient needs to be positioned to maximize circulation during treatment; (4) a dressing that seals the area and prevents the escape of moisture should be applied after treatment; (5) an intensity of 1.5 W/cm2 should be used to capture both the thermal and nonthermal effects of the US; and (6) low-intensity US (0.5 W/cm2) should be used when treating open wounds or acute injuries. Research is needed to clarify what parameters of US will most efficiently facilitate topical drug diffusion, how often and for what duration US should be used to maximize local absorption of drugs, and which topical drugs can most effectively be used for phonophoresis.