Comparisons of different animal skins with human skin in drug percutaneous penetration studies

The in vitro penetration of theophylline, sodium diclofenac and benzoic acid through artificial cellulose membrane and eight animal skins was investigated. The intact animal skins including stratum corneum (SC) and viable epidermis were taken from frog, snake with or without scales, nude mice, Sprague-Dawley rat, porcine and human prepuce and thigh skin. The results indicated that the penetration was fastest through cellulose membrane and frog skin and slowest through human prepuce and thigh skin. The snake skin with scales slowed down the penetration rate more significantly than the scaled skin. Benzoic acid was the fastest penetrant through all animal skins. The permeable behaviors of sodium diclofenac through SC and intact skin of snake, porcine and human were compared. In porcine, sodium diclofenac penetrated through SC at a rate 33 times higher than through intact skin, but in snake and human skin, the rate through SC was only 2.2 and 1.6 times higher than through intact ones. This implies that both viable epidermis and SC were the major rate limiting barriers in drug penetration. DSC thermograms and IR spectra showed that the SC of snake, porcine and human thigh were very similar in structure and components. The study suggests that snake skin, porcine skin and human prepuce skin could replace the human skin in in vitro drug penetration experiments.