Drug example: Cholestyramine
Mechanism of action: Bile is an emulsifier, produced by the liver and later stored and concentrated in the gallbladder. As discussed previously, bile is important in the digestion of lipids. Cholesterol is a component of the bile acids in bile. In normal physiology, bile acids are reabsorbed by the gastrointestinal (GI) tract after they have aided in digestion. Bile acid resins, such as cholestyramine, are not absorbable by the GI tract. When a patient takes bile acid resins, the drug binds to the bile acids present in the intestine. The bile acids are now unable to be reabsorbed. As a result, the liver must use stored cholesterol to make new bile acids. This lowers the blood cholesterol levels.
Use: Bile acid resins can decrease LDL cholesterol by up to 25%. They may result in a small increase in HDL cholesterol.
Drug toxicity: Due to the mechanism of action being centered in the GI tract, bile acid resins have many GI side effects. Patients often complain of gas and abdominal bloating. This often limits their use, as patients are unwilling to continue treatment due to the side effects. Absorption of vitamin K, folate, and certain medications is decreased as a result of bile acid resin treatment.