Cholestyramine: Bile Acid Sequestrant for Cholesterol and Pruritus
Cholestyramine is an anion exchange resin (bile acid sequestrant) that has been used since the 1960s for the treatment of hypercholesterolaemia. Unlike statins or ezetimibe, cholestyramine is not absorbed systemically, acting exclusively within the gastrointestinal lumen. This makes it one of the few lipid-lowering agents considered safe in pregnancy.
Beyond lipid lowering, cholestyramine is used to relieve the intractable itching (pruritus) associated with cholestatic liver diseases, where elevated bile acid levels in the skin cause severe pruritus. It is also occasionally used to treat C. difficile-associated diarrhoea and to bind certain drugs or toxins in the gut.
Mechanism of Action
Cholestyramine is a quaternary ammonium compound that forms a strong non-absorbable complex with bile acids in the intestinal lumen. Normally, approximately 95 percent of bile acids are reabsorbed from the terminal ileum and recycled back to the liver (enterohepatic circulation). By binding bile acids and preventing their reabsorption, cholestyramine increases faecal bile acid excretion. The liver responds to bile acid depletion by upregulating LDL receptor expression and increasing conversion of cholesterol to new bile acids, resulting in decreased circulating LDL cholesterol levels. In cholestatic pruritus, reducing intestinal bile acid load and systemic bile acid levels alleviates skin accumulation of pruritogenic bile acid metabolites.
Indications
Cholestyramine is approved for primary hypercholesterolaemia (type IIa hyperlipoproteinaemia) as monotherapy or adjunct to diet, and in combination with statins for patients not achieving LDL targets. It is used for symptomatic relief of pruritus in partial biliary obstruction, primary biliary cholangitis, and other cholestatic liver diseases. In certain countries, cholestyramine is approved as adjunct therapy for bile acid diarrhoea following ileal resection. Off-label uses include management of C. difficile recurrence and cholestyramine-responsive diarrhoea.
Dosage and Administration
Standard dose: four grams (one sachet) once to three times daily, typically not exceeding 24 grams per day. The powder must be mixed with at least 150 mL of water, juice, soup, or other liquid and stirred thoroughly before drinking; it must never be taken dry due to oesophageal obstruction risk. To minimise drug interactions, cholestyramine should be taken at least one hour before or four to six hours after other medications. Initial doses should be low and increased gradually to improve gastrointestinal tolerability. Long-term treatment should be accompanied by fat-soluble vitamin supplementation (A, D, E, K) as cholestyramine reduces their absorption.
Side Effects
Gastrointestinal complaints are the predominant adverse effects and are dose-related: constipation is extremely common and can be severe, particularly in elderly patients; bloating, flatulence, nausea, and abdominal pain are frequent. The constipation can sometimes paradoxically worsen the pruritus of cholestasis. Fat-soluble vitamin deficiencies (A, D, E, K) develop with long-term unsupplemented use, leading to night blindness, osteoporosis, coagulopathy, and neuropathy. Hypertriglyceridaemia can develop or worsen as a secondary response to increased bile acid synthesis. The resin does not cause systemic side effects as it is not absorbed.
Interactions
Cholestyramine binds many anionic drugs in the intestine, significantly reducing their absorption. Affected drugs include levothyroxine, digoxin, warfarin, statins, thiazide diuretics, furosemide, propranolol, and fat-soluble vitamins. The standard recommendation is to take other medications at least one hour before or four to six hours after cholestyramine. The interaction with warfarin is particularly important as both reduced and enhanced anticoagulant effects have been reported; close INR monitoring is required.
Special Notes
Cholestyramine is not absorbed and does not cross the placenta, making it one of the few lipid-lowering options considered in pregnancy-associated hypercholesterolaemia, though evidence is limited. It is contraindicated in complete biliary obstruction (no bile acid enters the gut to bind) and in hypersensitivity to any component. Adequate fluid intake must be maintained during treatment. In practice, poor palatability and tolerability are major barriers to adherence. Colesevelam is a newer bile acid sequestrant with better tolerability and fewer drug interactions.
Related Topics
Frequently Asked Questions
Why must cholestyramine be mixed with liquid before taking it?
Cholestyramine is a dry powder that can swell and cause oesophageal obstruction or choking if swallowed without sufficient liquid. Always mix thoroughly with at least 150 mL of water, juice, or another suitable liquid and consume immediately. The powder should not be inhaled during preparation as it can cause respiratory irritation.
How does cholestyramine reduce cholesterol?
Cholestyramine binds bile acids in the intestine and prevents their reabsorption. The liver must then convert more cholesterol into bile acids to replace the lost pool. To supply cholesterol for this synthesis, the liver upregulates LDL receptors, removing more LDL from the circulation. This sequence reduces LDL cholesterol by 15 to 30 percent as monotherapy.
Why does cholestyramine interact with so many medications?
Cholestyramine is a non-specific ion exchange resin that binds negatively charged (anionic) molecules in the gut. Many drugs have anionic groups at intestinal pH and are bound by cholestyramine, preventing their absorption. The binding is not drug-specific, which is why nearly any oral medication taken simultaneously with cholestyramine may have reduced bioavailability.
Sources
- EMA: Cholestyramine Summary of Product Characteristics 2023
- ESC Dyslipidaemia Guidelines 2022
- EASL Clinical Practice Guidelines on Cholestasis 2022