The influence of ultrasound on the percutaneous absorption of benzydamine hydrochloride from a gel base was investigated in a double-blind, placebo-controlled clinical study of 10 healthy volunteers. Using two similar experimental protocols, the effect of both 1:1 (2 msec on, 2 msec off) pulsed-output ultrasound (3.0 MHz at 1.0 W/cm2 and 0.0 W/cm2 [control]) and continuous-output ultrasound at a range of frequencies (0.75, 1.5, and 3.0 MHz at 1.5 W/cm2) were investigated. A placebo control (benzydamine gel massaged with ultrasound applicator switched off) was incorporated into each protocol. Percutaneous absorption of benzydamine was assessed by measurement of the residual amount of drug in the formulation base after treatment. Drug assay was by reversed-phase high-performance liquid chromatography and ultraviolet detection. Statistical analysis of the results for both continuous and pulsed ultrasound treatment showed that no significant differences existed between data for ultrasound treatment versus no ultrasound. In conclusion, although phonophoresis has been alleged to enhance percutaneous absorption of numerous drugs, ultrasound did not enhance the percutaneous absorption of benzydamine under the experimental conditions of this study.
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