Transdermal Delivery and Analgesic Effects of Lidocaine Hydrogel by Phonophoresis

To investigate the permeability of lidocaine, percutaneous absorption studies were performed using excised hairless mouse skin and the penetration of lidocaine via the skin was determined. To increase the skin permeation of lidocine, the effects of $Labrasol^{(R)}$, $Labrafil^{(R)}$, $Labrafac^{(R)}$ and $Transcutol^{(R)}$ were investigated. The skin permeation of lidocaine was increased when $Labrasol^{(R)}$ and $Transcutol^{(R)}$ were used as permeation enhancer. To evaluate the influence of ultrasound, various factors such as application modes (continuous mode and pulsed mode), frequency (1.0 and 3.0 MHz) and intensity (1.0, 1.5 and 2.0 w/$cm^2$) were investigated with lidocaine hydrogel. The pronounced effect of ultrasound on the skin permeation of lidocaine was observed at all ultrasound energy levels. The influence of frequency having an effect on skin permeation rate was higher in the case of using 1 MHz, 2.0 w/$cm^2$ and continuous treatment. As the intensity of ultrasound increased, the permeation of lidocaine was accelerated. The in vivo anesthetic effects were evaluated by two aspects as mechanical threshold and electrical threshold. Six healthy volunteers consented to the randomized, double-blind, and cross-over designed study in each group. In each subject, 3 groups were adapted such as K group (ultrasound with gel base only), L group (lidocaine gel) and B group (ultrasound with lidocaine gel). In conclusion, lidocaine was potent anesthetic which could be block pain threshold effectively. And ultrasound could accelerate the skin penetration of lidocaine. The phonophoretic delivery system could be a good candidate for lidocaine as a local anaesthetic to improve the skin permeation and in vivo anaesthetic effect.

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