Bile acid sequestrant
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The '''bile acid sequestrants''' are a group of medications used for binding certain components of [[bile]] in the [[gut|gastrointestinal tract]]. They disrupt the [[enterohepatic circulation]] of [[bile acid]]s by sequestering them and preventing their reabsorption from the gut. They are generally classified as [[hypolipidemic agent]]s, although they may be used for purposes other than lowering cholesterol.
==Mechanism of action==
Bile acid sequestrants are [[polymer]]ic compounds which serve as [[ion exchange resin]]s. Bile acid sequestrants exchange [[anion]]s such as [[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]].<ref>[http://www.fda.gov/hearthealth/treatments/medications/bileacid.html FDA Heart Health Online - Bile Acid Sequestrants<!-- Bot generated title -->]</ref>
==Indications==
Since bile acids are biosynthesized from [[cholesterol]], the disruption of bile acid reabsorption will decrease cholesterol levels, particularly [[low density lipoprotein]] (commonly known as "bad cholesterol"). Therefore, they may be used for the treatment of [[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 [[polymer]]ic resins:
* [[Cholestyramine]] (Questran)
* [[Colesevelam]]<ref name="pmid11975771">{{cite journal |author=Wong NN |title=Colesevelam: a new bile acid sequestrant |journal=Heart disease (Hagerstown, Md.) |volume=3 |issue=1 |pages=63–70 |year=2001 |pmid=11975771 |doi=}}</ref> (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]]s, such as [[vitamin A]], [[vitamin D]], [[vitamin E]], and [[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 [[hypolipidemic agent]]s has decreased markedly since the introduction of the [[statin]]s, which are more efficacious than bile acid sequestrants at lowering [[LDL]]. They are occasionally used as an adjunct to the statins; this is because the [[fibrate]]s (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==
<references/>
{{Lipid modifying agents}}
[[Category:Hypolipidemic agents]]
[[Category:Hepatology]]
[[pt:Sequestrador de ácidos biliares]]
[[th:ไบล์แอซิดซีเควสแตนต์]]