Advanced harmonization techniques result in accurate establishment of in vitro-in vivo correlations for oxybenzone...

Due to high variability during clinical pharmacokinetic (PK) evaluation, the prediction of in vivo exposure from in vitro absorption testing of topical semisolid and liquid dermal products has historically proven difficult. Since absorption from unoccluded formulations can be influenced by environmental factors such as temperature and humidity, maximal effort must be placed on the harmonization of experimental parameters between in vitro and in vivo testing conditions to establish accurate in vitro/in vivo correlations (IVIVC). Using four different sunscreen formulations as a model, we performed in vitro permeation testing (IVPT) studies with excised human skin and maintained strict harmonization techniques to control application time, occlusion, temperature, and humidity during in vivo human serum PK evaluation. The goal was to investigate if increased control over experimental parameters would result in decreased inter-subject variability of common topical formulations leading to acceptable IVIVC establishment. Using a deconvolution-based approach, excellent point-to-point (Level A correlation) IVIVC for the entire 12-h study duration was achieved for all four sunscreen formulations with < 10% prediction error of both area under the curve (AUC) and peak concentration (C_max) estimation. The low variability of in vivo absorption data presents a proof-of-concept protocol design for testing of complex semisolid and liquid topical formulations applied over a large surface area with reapplication in a reliable manner. This work also presents the opportunity for expanded development of testing for the impact of altered temperature and humidity conditions on product absorption in vivo with a high degree of precision.