Absorption of sunscreens and other compounds through human skin in vivo : derivation of a method to predict maximum fluxes

The goal of this study was to quantify the transdermally absorbed amounts of the sunscreens octyl dimethyl p-aminobenzoic acid, oxybenzone, 4-isopropyl-dibenzoylmethane, 3-(4-methylbenzylidene)-camphor, isoamyl-4-methoxycinnamate, the repellent and plasticizer dibutyl phthalate, the antioxidant 3.5-di-t-butyl-4-hydroxyanisol, and the antimicrobial compounds butyl-4-hydroxybenzoate, biphenyl-2-ol, and 2,4,4'-tri-chlor-2'-hydroxydiphenylether (triclosane). Permeabilities PB and maximum fluxes Jmax should be correlated with relevant physicochemical properties. Saturated solutions of the above-mentioned compounds in a propylene glycol/water mixture were applied to the skin using glass chambers which were fixed to the upper arms of volunteers. Maximum fluxes were calculated from concentration decreases in the vehicle. A linear relationship between the logarithms of permeabilities PB of the penetrants (0.02-0.28 cm h-1) and the corresponding octanol/vehicle partition coefficients PCOct/V (166-186,208) was found. Consequently, the influence of aqueous boundary layers could be neglected. However, the slope of the resulting straight line of 0.38 is considerably smaller than unity indicating that PCOct/V does not represent the lipophilicity of the stratum corneum adequately. Maximum fluxes range from 0.5 to 130 micrograms cm-2 h-1. A general equation for the calculation of Jmax was derived based on experimental data taking into account the PCOct/V and the solubilities CsV of the respective penetrants in the vehicle.