Bile acid sequestrants are one of the oldest lipid-lowering drug classes, yet they remain high-yield for exams because of their unique gut-based mechanism, characteristic GI side effects, and classic role in cholestatic pruritus and bile-acid diarrhea.
What Are Bile Acid Sequestrants?
Bile acid sequestrants are non-absorbed resins that bind bile acids in the intestine, preventing their reabsorption.
One-Line Definition
Bile acid sequestrants lower LDL cholesterol by binding bile acids in the gut and increasing hepatic cholesterol utilization
Why Bile Acids Matter
1. Bile acids are synthesized from cholesterol in the liverIf bile acids are lost in stool, the liver must use more cholesterol to make new bile acids → LDL falls
Mechanism of Action (Very High-Yield)
Step-by-Step
1. Drug binds bile acids in the intestineOne-Line Exam Answer
Bile acid sequestrants lower LDL by interrupting enterohepatic bile acid recycling
Effects on Lipid Profile
| Lipid | Effect |
|---|---|
| LDL cholesterol | ↓↓ |
| HDL cholesterol | ↑ (mild) |
| Triglycerides | ↑ (can worsen) |
Important: These drugs can increase triglycerides.
Main Drugs in This Class
Cholestyramine
Prototype bile acid resin
Key Features
- Powder form
- Strong bile acid binding
- Non-absorbed
Clinical Uses
- Hypercholesterolemia (LDL reduction)
- Cholestatic pruritus (very high-yield)
- Bile acid diarrhea
- Adjunct in Graves’ disease (↓ thyroid hormone recycling)
Exam Pearl
✔ Drug of choice for pruritus due to obstructive jaundice
Colestipol
Key Features
- Similar to cholestyramine
- Slightly better tolerability
Uses
- Hypercholesterolemia
- Alternative to cholestyramine
Colesevelam
Key Features
- Newer agent
- Better GI tolerability
- Tablet form available
Uses
- Hypercholesterolemia
- Type 2 diabetes (improves glycemic control)
Exam Pearl
✔ Best tolerated bile acid sequestrant
High-Yield Comparison Table
| Feature | Cholestyramine | Colestipol | Colesevelam |
|---|---|---|---|
| Potency | High | Moderate | Moderate |
| GI tolerance | Poor | Moderate | Best |
| Form | Powder | Powder | Tablet |
| Diabetes benefit | No | No | Yes |
Clinical Uses of Bile Acid Sequestrants
Lipid Disorders
- Mild–moderate hypercholesterolemia
- Used when statins are contraindicated
Non-Lipid Uses (Exam Favorites)
- Cholestatic pruritus
- Bile acid–induced diarrhea
- Thyroid hormone excess (adjunct)
Advantages of This Drug Class
✔ Not systemically absorbed
✔ Safe in pregnancy
✔ No muscle toxicity
✔ Can be combined with statins (with caution)
Adverse Effects (Very Important)
Gastrointestinal
- Constipation
- Bloating
- Flatulence
- Abdominal discomfort
Metabolic
↑ TriglyceridesNutritional
↓ Absorption of fat-soluble vitamins (A, D, E, K)Drug Interactions (Exam Gold)
Bile acid sequestrants reduce absorption of:
- Warfarin
- Digoxin
- Thyroxine
- Fat-soluble vitamins
Rule: Give other drugs 1 hour before or 4–6 hours after
Contraindications
❌ Hypertriglyceridemia
❌ Complete biliary obstruction
❌ Severe constipation
Bile Acid Sequestrants vs Other Lipid Drugs
| Feature | BAS | Statins | Ezetimibe |
|---|---|---|---|
| Site of action | Intestine | Liver | Intestine |
| LDL lowering | Moderate | Strong | Moderate |
| TG effect | ↑ | ↓ | Neutral |
| Pregnancy safe | Yes | No | No |
Important Exam-Oriented Pearls
- Only lipid drugs safe in pregnancy
- Cause constipation
- Increase triglycerides
- Used for cholestatic itching
- Do not enter bloodstream
Easy Memory Tricks
- “CHOLESTYRAMINE traps bile like a net”
- “BILE goes out → LDL goes down”
- “Resins = Rough on the gut”
FAQs
1. What is the main action of bile acid sequestrants?
They bind bile acids in the intestine and lower LDL cholesterol.
2. Which lipid is mainly reduced?
LDL cholesterol.
3. Can bile acid sequestrants increase triglycerides?
Yes, they can.
4. Which drug is best tolerated?
Colesevelam.
5. Which bile acid sequestrant is used for pruritus?
Cholestyramine.
6. Are these drugs absorbed systemically?
No, they act only in the gut.
7. Are bile acid sequestrants safe in pregnancy?
Yes.
8. Why do they cause constipation?
Due to bile acid binding and gut effects.
9. Do they interfere with other drugs?
Yes, they reduce absorption of many medications.
10. Are they first-line lipid-lowering drugs?
No, statins are first-line.
