In Vitro Testing of Sunscreens for Dermal Absorption: Method Comparison and Rank Order Correlation with In Vivo Absorption.

Evaluating the dermal absorption of sunscreen UV filters requires the development of a bio-predictable in vitro permeation test (IVPT). This work describes the comparison of two IVPT methods and rank order correlations of in vitro absorption (skin permeation and retention) with the in vivo absorption (AUC and skin retention) of sunscreens. The IVPT was compared regarding the following elements: (1) application of a single finite dose vs. an infinite dose and (2) the use of heat-separated human epidermis vs. dermatomed skin models. The IVPT was used to evaluate dermal absorption of six UV filters (avobenzone, homosalate, octinoxate, octisalate, octocrylene, and oxybenzone) in commercial sunscreens. Both the in vivo and in vitro permeation studies demonstrated that all UV filters were absorbed following a single-dose application. Sunscreens were rank ordered by the amount of the UV filters absorbed. Data obtained from the IVPT method using a single finite dose and heat-separated human epidermis was found to correlate with the clinical data. Rank orders of the cumulative in vitro skin permeation and the in vivo AUC were found comparable for oxybenzone, homosalate, octisalate, and octinoxate. Rank orders of the in vitro and in vivo skin retention of oxybenzone and octinoxate were also comparable. Additional IVPT parameters may be optimized to enhance the discriminatory power for UV filters with low skin permeation potential (e.g., avobenzone and octocrylene).