Mechanistic studies of ultrasonically enhanced transdermal drug delivery

The transdermal route of drug delivery offers a noninvasive and painless alternative to more traditional routes such as injections. However, its applicability is limited to only a handful of drugs due to the low permeability of the skin. It has been demonstrated that low‐frequency ultrasound significantly enhances transdermal transport of a variety of drugs (sonophoresis). There is strong experimental evidence to suggest that cavitation plays a key role in this enhancement, although it is not clear which cavitational effects are primarily responsible for the transport. Cavitation can affect transdermal transport in at least two ways: It can induce changes in skin structure, creating pathways or channels for molecules to diffuse across and/or it can induce convective transport across the skin. An experimental system has been developed to assess contributions due to each of these phenomena individually. Although the data are insufficient to eliminate a role for convective processes, these experiments clearly indicate that stuctural changes in the skin play an important, and probably primary, role in enhanced transport.