Effect of passive and iontophoretic skin pretreatments with terpenes on the in vitro skin transport of piroxicam.

The enhancing effect of several terpenes (thymol, menthone and 1,8-cineole) in the percutaneous permeation of piroxicam (Px), either passive or iontophoretically, was investigated. These terpenes were applied, on the skin membrane, as a passive and iontophoretic skin pretreatment. Px was delivered from carbopol gels containing hydroxypropyl-beta-cyclodextrin (2% w/w Px). An increase in Px flux values, both passive and iontophoretic after skin pretreatment with 5% terpenes/50% EtOH, was found to be in the following order: thymol>menthone>1,8-cineole. Iontophoretic skin pretreatment with terpenes produced a slight increase in the passive flux of Px, in comparison with the passive skin pretreatment. This result indicated that iontophoresis could modify the skin morphology and consequently, increase the passive transport of Px. However, when Px was transported iontophoretically, passive skin pretreatment with terpenes, produced higher flux values than iontophoretic skin pretreatment. These results could be explained by the fact that with the iontophoretic pretreatment, terpenes could penetrate into the skin and limitate the movement of the ionized species, across the skin, during the iontophoretic experiments. The amount of Px retained in the skin after all experiments was related to flux values across skin.