the effect of bubble surface charge on phonophoresis

it is over several decades that ultrasound is used to enhance the transdermal drug delivery (phonphoresis). the mechanism of the enhancement is not fully understood and the ability of ultrasound on the enhancement for some drugs is unclear. the effect of continuous wave 870 khz ultrasound at intensity of 1 w/cm 2 for 15 minutes on transdermal absorption of piroxicam from solution and gel formulations in hairless rat skin was studied. exposure to ultrasound increased the rate of diffusion from gel and solution of piroxicam to 10 and 3 times higher than that in skins not exposed to ultrasound. we strongly believe that the lower diffusion of piroxicam from solution is caused by the presence of extra bubbles generated by ultrasound. it can be suggested that cavitation activity and its negative surface charges play a dominant rule in phonophoresis.