Bile Acid Sequestrant – Mechanism & Uses
Bile acid sequestrants are medications that bind bile acids in the intestine, reducing cholesterol levels in the blood. They are used to treat elevated LDL cholesterol.
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Bile acid sequestrants are medications that bind bile acids in the intestine, reducing cholesterol levels in the blood. They are used to treat elevated LDL cholesterol.
What is a Bile Acid Sequestrant?
A bile acid sequestrant (also known as a bile acid binding resin or anion exchange resin) is a medication used to lower elevated cholesterol levels in the blood. These agents are non-absorbable polymer resins that bind bile acids in the gastrointestinal tract, preventing their reabsorption into the bloodstream. Common active ingredients in this drug class include cholestyramine, colestipol, and colesevelam.
Mechanism of Action
Bile acids are synthesized in the liver from cholesterol and released into the small intestine, where they assist in fat digestion. Under normal circumstances, approximately 95% of bile acids are reabsorbed in the terminal ileum (the final section of the small intestine) and transported back to the liver – a process known as the enterohepatic circulation.
Bile acid sequestrants interrupt this cycle by tightly binding bile acids within the intestinal lumen and facilitating their excretion in the stool. The liver must then synthesize additional bile acids from cholesterol, which depletes the cholesterol content within liver cells. In response, the liver upregulates the number of LDL receptors on its surface, increasing the uptake of LDL cholesterol from the bloodstream. This typically reduces LDL cholesterol levels by 15–30%.
Indications
Bile acid sequestrants are indicated for:
- Hypercholesterolaemia: elevated LDL cholesterol, particularly when statins are not tolerated or are insufficient
- Combination therapy: alongside statins in patients at high cardiovascular risk
- Cholestasis-related pruritus: cholestyramine is used to relieve itching caused by bile acid accumulation due to cholestasis
- Bile acid malabsorption: in patients with excessive bile acid entry into the colon following bowel surgery (bile acid diarrhoea)
Dosage and Administration
Bile acid sequestrants are taken orally, usually as a powder dissolved in water or juice, or as tablets (e.g., colesevelam). They should ideally be taken with meals, as bile acid binding is most effective when dietary fat is present to stimulate bile acid secretion. Since resins may also bind other medications in the gastrointestinal tract, other drugs should be taken at least 1 hour before or 4–6 hours after the resin to avoid impaired absorption.
Side Effects
Since bile acid sequestrants are not absorbed into the bloodstream, systemic side effects are rare. Most adverse effects involve the gastrointestinal tract:
- Constipation – the most common side effect
- Bloating and flatulence
- Nausea and abdominal discomfort
- With long-term use: possible reduced absorption of fat-soluble vitamins (A, D, E, K) and folic acid
- Elevation of triglyceride levels, particularly in patients with pre-existing hypertriglyceridaemia
Contraindications
Bile acid sequestrants should not be used in patients with:
- Complete biliary obstruction (bile duct blockage without bile flow into the intestine)
- Severe hypertriglyceridaemia
- Known hypersensitivity to the active ingredient
Drug Interactions
Due to their binding properties, bile acid sequestrants can impair the absorption of numerous medications, including:
- Thyroid hormones (e.g., levothyroxine)
- Cardiac glycosides (digoxin)
- Vitamin K antagonists (e.g., warfarin, phenprocoumon)
- Thiazide diuretics and beta-blockers
- Fat-soluble vitamins
Therefore, appropriate time intervals between the administration of bile acid sequestrants and other medications must always be maintained.
References
- Loscalzo J. et al. (eds.) – Harrison's Principles of Internal Medicine, 21st edition, McGraw-Hill Education, 2022
- Catapano AL et al. – 2019 ESC/EAS Guidelines for the management of dyslipidaemias. European Heart Journal, 2019; 41(1):111–188. DOI: 10.1093/eurheartj/ehz455
- European Medicines Agency (EMA) – Product information for cholestyramine, colestipol, and colesevelam. Available at: www.ema.europa.eu
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