Barrier function of intact and impaired skin: percutaneous penetration of caffeine and salicylic acid

Background Normally, percutaneous absorption tests are carried out using skin biopsies for an apparent and acceptable physiological condition. However, under different pathological conditions, the stratum corneum (SC) barrier function is impaired. Methods The barrier function of the SC was assessed by correlation between the number of repeated applications of tape strips on the skin and its transepidermal water loss (TEWL), as well as by in vitro percutaneous absorption studies of different compounds, using Franz diffusion cells and porcine skin previously stripped. Results A progressive diminution of the skin barrier function has been detected by TEWL both in vitro and in vivo as the number of skin tape strips increases. On the other hand, the percutaneous absorption of the compounds tested increases in a different way as the number of strips increases. Salicylic acid increases linearly depending on the barrier disturbance. However, percutaneous absorption of caffeine exponentially increased with barrier disturbance. Our results indicate that the barrier impairment of skin always increases the penetration behavior of a given compound; however, the hydrophilic–lipophilic balance of the compounds or formulations used could greatly modify its penetration profile, especially when a modified skin is used. Conclusions This in vitro protocol may be useful to simulate the percutaneous absorption profile of some drugs applied onto skin with an impaired SC barrier function and could be used to avoid, to some extent, the use of in vivo experimental animal models in the dermopharmaceutical field.