Assessment of in vitro percutaneous absorption of glycolic acid through human skin sections using a flow-through diffusion cell system

Abstract

The percutaneous absorption studies were performed using a flow-through diffusion cell system with skin specimens from 24 healthy women to assess the penetration of glycolic acid (GA). Percentages of GA, based on 14C-labelled activity, found in the skin after application of 4% GA at pH 2.0 or pH 3.8, after 24 h were as follows: stratum corneum (SC) = 2.65 ± 1.80 versus 1.13 ± 1.14 ( P < 0.05); viable skin (VS) = 13.46 ± 7.44 versus 2.23 ± 1.51 ( P < 0.05) and effluent fraction (EF) = 12.22 ± 9.03 versus 1.42 ± 0.77 ( P < 0.05), respectively. The applications of 4–60% GA at their native pH resulted in an increased penetration of GA through the skin. For example, application of 20% GA, pH 1.9, resulted in the following values: SC = 2.69 ± 2.26 ( P > 0.05); VS = 4.88 ± 4.05 ( P > 0.05) and EF = 30.69 ± 13.25 ( P < 0.05). Duration of application also affected the extent of penetration of drug. For example, application of 20% GA, pH 1.9, for 6 h resulted in the following levels: SC = 1.16 ± 0.80 ( P < 0.05); VS = 4.07 ± 1.78 ( P > 0.05) and EF = 6.12 ± 4.95 ( P < 0.05). In conclusion: (i) absorption of GA in human skin are pH-, strength- and time-dependent; and (ii) the in vitro method appears to provide an appropriate model to reflect in vivo absorption of GA through human skin.