An in vitro percutaneous absorption study of non-ionic compounds across human skin.

Generally, the mechanisms of percutaneous absorption are studied from correlations between representative penetration parameters (permeability coefficients) and variables accounting for lipophilicity or other related physicochemical properties. The present study was developed on the basis of the in vitro permeability coefficients through human skin, 280 microns in thickness, of a non-ionic homologous series of compounds (phenylalkanols). The corresponding penetration/lipophilicity correlations were compared with those found for a basic homologous series (4-n-alkylanilines) through a membrane of similar characteristics. The in vitro behaviour of both series of compounds may be regarded as similar. Differences were only observed in the permeability coefficients of those elements which in both series exhibited lipophilicity values above that considered optimum, as predicted by the selected biophysical penetration model. Consequently, it appears that the removal of the thick dermal tissue leads to increased permeation rates for the more lipophilic compounds and suggests that the dermis acts as an aqueous matrix.