Percutaneous absorption: a new physicochemical predictive model for maximum human in vivo penetration rates

A diffusion model for stratum corneum-limited percutaneous absorption based on the interaction of the diffusate with the stratum corneum was derived. Two types of interactions were proposed, ion-dipole and lipid-lipid, based on current knowledge of the stratum corneum and on irreversible thermodynamic arguments. The resulting flux equations predict a linear dependence of flux on the dipole moment and ln X of the diffusates , where X is the mole fraction solubility. These flux equations were tested on 21 different diffusates whose human percutaneous absorption rates in vivo had been previously determined. A solubility method was used to classify the interaction pathway for each diffusate . Correlation of the maximum absorption rate for the lipid and polar pathways give correlation coefficients of 0.946 and 0.998, respectively. It is believed that these studies provide a starting point for the ultimate goal of percutaneous absorption research: to be able to bypass in vivo and in vitro studies and to predict absorption solely on the basis of the physicochemical properties of the diffusates .