The bile-sequestering drugs are cholestyramine, colestipol, and colesevelam. These drugs are resins that remove excess bile acids from the fat deposits under the skin.
Bile-sequestering drugs aren’t absorbed from the GI tract. Instead, they remain in the intestine, where they combine with bile acids for about 5 hours. Eventually, they’re excreted in stool.
The bile-sequestering drugs lower blood levels of low-density lipoproteins (LDLs). These drugs combine with bile acids in the intestines to form an insoluble compound that’s then excreted in stool. The decreasing level of bile acid in the gallbladder triggers the liver to synthesize more bile acids from their precursor, cho-lesterol.
As cholesterol leaves the bloodstream and other storage areas to replace the lost bile acids, blood cholesterol levels decrease. Be-cause the small intestine needs bile acids to emulsify lipids and form chylomicrons, absorption of all lipids and lipid-soluble drugs decreases until the bile acids are replaced.
Bile-sequestering drugs are the drugs of choice for treating type IIa hyperlipoproteinemia (familial hypercholesterolemia) when the patient can’t lower his LDL levels through diet alone. Patients whose blood cholesterol levels place them at a severe risk of CAD will most likely require one of these drugs in addition to dietary changes.
Bile-sequestering drugs produce the following drug interactions:
§ They may bind with acidic drugs in the GI tract, decreasing their absorption and effectiveness. Acidic drugs likely to be affected in-clude barbiturates, phenytoin, penicillins, cephalosporins, thyroid hormones, thyroid derivatives, and digoxin.
§ Bile-sequestering drugs may decrease absorption of propra-nolol, tetracycline, furosemide, penicillin G, hydrochlorothiazide and gemfibrozil.
§ Bile-sequestering drugs may reduce absorption of lipid-soluble vitamins, such as vitamins A, D, E, and K. Poor absorption of vita-min K can affect prothrombin times significantly, increasing the risk of bleeding. (See Adverse reactions to bile-sequesteringdrugs.)