In vitro study of low-frequency ultrasound-enhanced transdermal transport of fentanyl and caffeine across human and hairless rat skin

The effect of low-frequency sonophoresis on fentanyl and caffeine permeatio n through human and hairless rat skin was studied in vitro. Experiments wer e performed using 20 kHz ultrasound applied at either continuous or discont inuous mode and with an average intensity of 2.5 W/cm(2). The results showe d that low-frequency ultrasound enhanced the transdermal transport of both fentanyl and caffeine across human and hairless rat skin. This was explaine d by both increasing flux during sonication and shortening the lag time. Di scontinuous mode was found to be more effective in increasing transdermal p enetration of fentanyl while transdermal transport of caffeine was enhanced by both continuous and pulsed mode. Histological and electron microscopy s tudies showed that human and hairless rat skin was unaffected by ultrasound exposure. Further studies will be necessary to determine the relative cont ribution of ultrasound parameters in low-frequency ultrasound-induced percu taneous enhancement of drug transport. (C) 2001 Elsevier Science B.V. All r ights reserved.