Part 2 book “Predictive methods in percutaneous absorption” has contents: Algorithms for estimating permeability across artificial membranes, other approaches to modelling percutaneous absorption, squiggly lines and random dots—you can fit anything with a nonlinear model, the devil is in the detail, and other contents. | Chapter 5 Algorithms for Estimating Permeability Across Artificial Membranes The Role of Artificial Membranes in Studies of Percutaneous Absorption As discussed in Chap. 2, there are a range of established and validated in vitro methods for the measurement of percutaneous absorption. In general, in vitro experiments of the nature described in Chap. 2 will form a significant part of earlystage evaluation of pharmaceutical formulations or in risk assessment protocols. Their use is followed by, and informs, preclinical and clinical evaluation. While fresh human skin (either as full thickness skin, heat-separated epidermal tissue or skin dermatomed to a defined thickness) is the perceived “gold standard” for in vitro testing, it is not always available and certain well-defined compromises are commonly adopted, including the use of human skin that had previously been frozen. Moving further “backwards” from the idealised in vitro model leads to the use of animal tissue; while the use of tissue from a range of species (rat, mouse, pig, guinea pigs, snakes and various species of monkey) has been widely reported in the literature, it is accepted that pigskin is the best model for human skin, with the pig ear being widely used despite differences in the lateral packing of stratum corneum lipids and suggestions that it may have a lower barrier function than human skin (Petitot et al. 2007; Vallet et al. 2007; Caussin et al. 2008; Klang et al. 2012). In order to address the issue of tissue variation and availability, various cultured skin alternatives, based on the living skin equivalent models, have also been considered. This technology includes marketed products such as EpiDerm®, EpiSkin® and SkinEthic®. Reconstructed skin models have also been considered although they have been found to exhibit higher permeability than excised mammalian skin as they often have an incomplete or inconsistent barrier (Van Gele et al. 2011; Kuchler et al. 2013). In general, their use has not .
