Bile acid sequestrant

Mechanism of action

Bile acid sequestrants are chloride ions for bile acids. By doing so, they bind bile acids and sequester them from enterohepatic circulation.

Since bile acid sequestrants are large polymeric structures, they are not well-absorbed from the gut into the bloodstream. Thus, bile acid sequestrants, along with any bile acids bound to the drug, are excreted via the feces after passage through the gastrointestinal tract.^[1]

Indications

Since bile acids are biosynthesized from hypercholesterolemia and dyslipidemia.

In chronic liver diseases such as cirrhosis, bile acids may deposit in the skin, causing pruritus (itching). Hence, bile acid sequenstrants may be used for the prevention of pruritus in patients with chronic liver disease.

Additionally, diarrhea may be caused by excess bile salts entering the colon rather than being absorbed at the end of the small intestine, typically shortly after eating. Bile salt diarrhea is a possible side-effect of gallbladder removal. Bile acid sequestrants may reduce diarrhea in these patients.

Examples of bile acid sequestrants

Three drugs are members of this class; all are synthetic polymeric resins:

• Cholestyramine (Questran®)
• Colesevelam^[2] (Cholestagel® in Europe, WelcholTM in the USA)
• Colestipol (Colestid®)

Side effects

Since bile acid sequestrants are designed to stay in the gut, they generally do not have systemic side effects. However, they may cause problems in the gastrointestinal tract (GI tract), such as constipation, diarrhea, and flatulence. Some patients complain of the bad taste.

Drug interactions

In addition to bile acids, bile acid sequestrants may also bind drugs in the GI tract, preventing their absorption into the bloodstream. For this reason, it is generally advised that bile acid sequestrants be spaced several hours apart from other drugs.

They may also bind fat-soluble vitamin K. This effect may result in a vitamin deficiency. Hence, vitamin supplementation may be warranted.

Role in clinical use

Use of these agents as fibrates (another major group of cholesterol-lowering drugs) are thought to increase the risk of rhabdomyolysis when used with statins, and so this otherwise expectable combination is frequently avoided.

Additionally, because bile acid sequestrants are not well-absorbed from the gut, they are generally regarded as being safe in pregnant women. However, by interfering with vitamin absorption, they may cause vitamin deficiencies that may affect the fetus. Hence, vitamin supplementation may be warranted, with appropriate intervals between dosing of the vitamins and bile acid sequestrants.

References

1. ^ http://www.fda.gov/hearthealth/treatments/medications/bileacid.html
2. ^ Wong NN (2001). "Colesevelam: a new bile acid sequestrant". Heart disease (Hagerstown, Md.) 3 (1): 63–70. PMID 11975771.