Transdermal drug delivery offers various advantages over conventional drug delivery systems, such as avoidance gastrointestinal degradation and hepatic first-pass effect, encourages patient compliance, and possible sustained release of drugs. However, transdermal transport of drugs is low permeability of the stratum corneum, the superficial layer of the skin. Many physicochemical and biological factors influencing transdermal transport is described together with the corresponding experimental and clinical results.
Phonophoresis is medical treatment with drugs introduced into the skin by ultrasound energy. Enhanced drug penetration is through to result from the biophysical alterations of skin structure by ultrasound waves. The frequency used for phonophoresis is usually from 20 xffi to 15ft. Phonophoresis can be categorized into three ranges: low-frequency range(below I MHz), therapeutic frequency range(1 to 3i Hz), and high-frequency range(above 3MHz). The depth of penetration of ultrasound into skin is inversely proportional to the frequency. Cavitation may cause mechanical stress, temperature elevation, or enhanced chemical reactivity causing drug transport. One theory is that ultrasound affects the permeation of the stratum corneum lipid structure as the limiting step in permeating through the skin. The range of indications for phonophoresis is wide. A specific classification of the range of indications is obtained by classification of pathological conditions.
The continuous research is needed for many interesting issues of phonophoretic transdermal delivery in new future.
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