Ultrasound-induced transcutaneous transport for drug delivery and diagnostics

In spite of major research and development efforts in transdermal systems and the many advantages of the transdermal route, impermeability of the human skin is still a major problem that limits the usefulness of the transdermal drug delivery approach. Application of ultrasound induces temporary structural changes in the skin resulting in enhanced transdermal transport of molecules (sonophoresis). Experimental findings suggest that among all the ultrasound‐related phenomena evaluated, cavitation plays the dominant role in sonophoresis, suggesting that application of low‐frequency ultrasound should enhance transdermal transport more effectively. It was found that at the low ultrasound frequencies high molecular weight molecules including insulin, interferon, and erythropoietin can be transported through the skin. Recently it was shown that the enhanced skin permeability during sonophoresis also facilitates outward diffusion of glucose present in the interstitial fluids beneath the skin. The in vitro as well as in vivo experiments show that the amounts of glucose extracted by sonophoresis are proportional to the blood glucose concentrations. Furthermore, the amount of glucose extracted by ultrasound can be measured and used to predict temporal changes in the blood glucose levels. These results demonstrate the feasibility of developing a noninvasive method of drug delivery and diagnostics using ultrasound.