(3R,4S)-1-(4-fluorophenyl)-3-[(3R)-3-(4-fluorophenyl)-3-hydroxypropyl]-4-(4-hydroxyphenyl)-azetidin-2-one, with CAS number 163380-16-3, is the active pharmaceutical ingredient (API) known as Ezetimibe. It is a white to off-white crystalline powder. The compound features a unique azetidin-2-one (beta-lactam) core structure, which is distinct from the statin class of cholesterol-lowering drugs. Ezetimibe is a selective inhibitor of intestinal cholesterol absorption. It acts by binding to the Niemann-Pick C1-Like 1 (NPC1L1) protein on the surface of enterocytes in the small intestine, thereby blocking the uptake of dietary and biliary cholesterol. This mechanism of action is complementary to that of HMG-CoA reductase inhibitors (statins). It is primarily used, either alone or in combination with statins, for the treatment of primary hypercholesterolemia, homozygous familial hypercholesterolemia, and homozygous sitosterolemia, helping to reduce elevated levels of total cholesterol and low-density lipoprotein cholesterol (LDL-C). As a well-established API, Ezetimibe is formulated into oral tablets. Its development and manufacturing are subject to strict pharmaceutical regulatory standards (e.g., cGMP) to ensure purity, potency, and safety. Key quality attributes include control over stereochemistry and related substance profiles.