MDR3cyte® is a fully-validated assay format that characterizes MDR3 inhibition by a test agent using primary hepatocytes in suspension. This platform is metabolically competent and retains biological functions. The assay involves in situ biosynthesis of deuterium (d9)-labeled PC, activation of MDR3 by bile salt micelles and LC-MS/MS determination of transported extracellular d9-PC. The profile of PCs produced using the MDR3cyte® assay platform and human hepatocyte more accurately reflects the profile found in natural human bile. MDR3 inhibition is associated with most DILI-concern drugs.