Intestinal Drug Absorption: Cell-Free Permeation Systems

Intestinal tissue or cell layers are of great interest to investigate the intestinal permeation potential of drug compounds but their application in pharmaceutical industrial laboratories is strongly discouraged and complicated due to high ethical burdens and lengthy preparation steps. This necessitated (biopharmaceutical) scientists to spend efforts and resources on the development of alternative options to evaluate intestinal drug permeation which has resulted in the raise of numerous cell-free permeation tools during the last decade. While cell-based systems are still preferred for the assessment of the apparent drug permeability coefficient (Papp), which is a widely used indicator for the ability of the drug to pass across the biological membrane, there is a paradigm shift from the traditional cell- and tissue-based permeation barriers toward cell-free permeation barriers for combined dissolution-permeation evaluation in the context of formulation performance studies. Therefore, this chapter describes the history of the currently available cell-free permeation barriers supplemented with a state-of-the-art overview containing the most recent developments. A significant part of the chapter is dedicated to the predictive capacity of the in vivo situation with a specific focus on the application of these models in oral drug delivery; however, some case examples are also mentioned in the field of non-oral drug delivery.