To be able to produce the aimed therapeutical effect, the drug needs to reach its target. In vitro permeability assays are used to evaluate the capability of potential drug molecules to permeate across epithelial and endothelial barriers of the body. There are number of membrane transporters, which are involved in drug absorption, distribution, and elimination. Therefore, evaluation of transporter-mediated drug-drug interactions is required by the regulatory authorities to evaluate whether the compound is a substrate or an inhibitor of various transporters.
