➦ Human organic anion transporting polypeptide OATP1B3 (previously known as OATP8) is highly expressed in liver where it mediates the uptake of many different drugs from blood into hepatocytes. Endogenous compounds that are transported by OATP1B3 are bile salts like taurocholate. Most of the drugs identified as substrates for OATP1B3 are also transported by OATP1B1. Clinical relevance and DDIs to hepatic uptake have been noted for both OATPs. Therefore, the regulatory agencies decided that drugs eliminated significantly via the liver have to be tested as potential inhibitors (substrates) for hOATP1B3.