Effect of ultrasound application on skin metabolism of prednisolone 21-acetate

Purpose. The effect of ultrasound on skin penetration and metabolism of prednisolone (PN) and prednisolone 21-acetate (PNA) was investigated in the hairless mouse skin in vitro. Methods. The abdominal skin excised freshly was pretreated under different ultrasound intensities (4.32, 2.88, and 1.50 W/cm(2)) for 10, 30, and 60 min. The penetration/metabolism rate of PNA and its metabolite (PN) was then measured using a side-by-side diffusion cell. Results. The skin penetration of PN was enhanced by the ultrasound pretreatment. This enhancement was attributed to the decrease in the stratum corneum barrier capacity by ultrasound energy. The steady-state appearance rate of PN following the skin bioconversion of PNA decreased appreciably with increasing the product of the duration of pretreatment (D-p, min) and the intensity of ultrasound applied (I-u, W/cm(2)). When the product value was less than 40 W/cm(2) . min, the steady-state appearance rate of the PN hardly increased in spite of the penetration enhancement of PNA. Conclusions. These findings indicated a possible deactivation of the skin enzymes by ultrasound energy.