Predicting the Percutaneous Penetration of Cosmetic Ingredients

By: Sara Farahmand, PhD, University of Cincinnati College of Pharmacy; and Howard I. Maibach, MD, PhD, University of California School of Medicine

Posted: March 30, 2010, from the April 2010 issue of Cosmetics & Toiletries.

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Fick’s first law of diffusion describes steady-state diffusion through a membrane, as seen in Eq. 3.

J = K*D/h * C0     Eq. 3

In Eq. 3, K is the SC/formulation partition coefficient of the drug, D is its diffusion coefficient in the SC of path length h, and C0 is the concentration of the drug applied. Therefore, the dependency of plasma concentration on flux (J) allows a relation to the drug’s physicochemical properties. Meanwhile, as a component of drug clearance, volume of distribution is also related to a drug’s solubility characteristics, which emphasizes the correlation of plasma concentration with the structural features of drug molecules.

Here, using multiple regression analysis, an empirical model has been adapted for predicting the Cmax of transdermally administered drugs based on their physicochemical properties such as log koct, MW or molecular volume (MV) and hydrogen bonding descriptors.

Methods and Results
As with most transdermal study techniques, the proposed model was based on multiple regression analysis^{2, 8, 12} of the C_max of 10 drugs, excluding fentanyl and clonidine, against physicochemical parameters,8 which yielded Eq. 4 as the best-fitted model.