Which of the following is a bile acid resin (BAR)?

Cholestyramine is identified as a bile acid resin (BAR) because it functions by binding to bile acids in the intestine. This binding process prevents the reabsorption of bile acids back into the bloodstream, leading to an increased conversion of cholesterol into bile acids in the liver. As a result, bile acid resins like cholestyramine effectively lower LDL cholesterol levels and are used in the management of hyperlipidemia.

The other options listed—simvastatin, ezetimibe, and niacin—serve different roles in lipid management. Simvastatin is a statin that inhibits HMG-CoA reductase, thus lowering cholesterol production in the liver. Ezetimibe works by blocking the absorption of cholesterol in the intestine. Niacin, on the other hand, is a vitamin that modifies lipid profiles by decreasing liver production of VLDL and increasing HDL cholesterol. Therefore, cholestyramine stands out among them as the only drug classified specifically as a bile acid resin.