21.4 Cholesterol Absorption Inhibitors

Cholesterol Absorption Inhibitors

Cholesterol absorption inhibitors (CAIs) lower LDL cholesterol by blocking cholesterol uptake in the small intestine. They're a useful option for patients who can't tolerate statins or who need additional LDL lowering on top of statin therapy.

Key Features and Mechanism of Action

The primary drug in this class is ezetimibe (Zetia). It works by targeting a specific transporter protein called Niemann-Pick C1-Like 1 (NPC1L1) on the brush border of the small intestine. NPC1L1 is responsible for moving cholesterol from the intestinal lumen into enterocytes (intestinal cells).

Here's how the mechanism plays out:

1. Ezetimibe binds to NPC1L1, blocking it from transporting dietary and biliary cholesterol into enterocytes.
2. Less cholesterol reaches the liver from the gut.
3. The liver compensates by upregulating LDL receptors on its surface.
4. More LDL receptors means more LDL cholesterol gets pulled out of the bloodstream.
5. Serum LDL cholesterol levels drop.

This mechanism is completely different from statins, which inhibit cholesterol synthesis in the liver. That's why combining a CAI with a statin attacks cholesterol from two angles and can produce greater LDL reduction than either drug alone.

Indications, Side Effects, and Drug Interactions

Indications:

• Adjunct to diet and exercise for reducing elevated LDL cholesterol in primary hyperlipidemia
• Combination therapy with statins when additional LDL lowering is needed
• Monotherapy for patients who are statin-intolerant or have contraindications to statins

Common side effects:

• Gastrointestinal disturbances (diarrhea, abdominal pain, flatulence)
• Headache
• Myalgia (muscle pain), especially when combined with a statin
• Upper respiratory tract infections

CAIs are generally well-tolerated compared to many other lipid-lowering drugs. The side effect profile is relatively mild.

Drug interactions to watch for:

• Fibrates (e.g., fenofibrate, gemfibrozil): Concurrent use increases the risk of cholelithiasis (gallstones). Gemfibrozil specifically raises ezetimibe levels and should be avoided.
• Cyclosporine: Increases ezetimibe blood levels. If used together, monitor cyclosporine levels closely.
• Bile acid sequestrants (e.g., cholestyramine): Can reduce ezetimibe absorption. If both are prescribed, administer ezetimibe at least 2 hours before or 4 hours after the bile acid sequestrant.
• Warfarin: Monitor INR more frequently when starting or stopping a CAI, as changes in cholesterol metabolism can affect warfarin response.

Nursing Considerations

Before starting therapy:

• Obtain a complete medical history, including prior lipid-lowering therapy and medication allergies
• Assess baseline lipid profile and liver function tests (LFTs), particularly if the patient will also be on a statin

Administration:

• Give orally, with or without food
• Encourage the patient to take it at the same time each day for consistency
• Standard dose of ezetimibe is 10 mg once daily

Ongoing monitoring:

• Recheck lipid profile periodically (typically 4 to 12 weeks after initiation) to evaluate therapeutic response
• Monitor LFTs periodically, especially when CAIs are used in combination with statins
• Assess for muscle pain or weakness, which may indicate myopathy when combined with statin therapy

Lifestyle reinforcement:

• Reinforce that medication works best alongside a heart-healthy diet low in saturated fat and cholesterol
• Encourage regular physical activity and maintaining a healthy body weight
• Address other modifiable cardiovascular risk factors such as smoking and uncontrolled blood pressure

Patient Education Plan

What the medication does: Ezetimibe lowers LDL cholesterol by reducing how much cholesterol your body absorbs from food and bile in the intestine. It does not replace diet and exercise; it works alongside them.

How to take it:

• Take exactly as prescribed, once daily, at the same time each day
• Continue taking it even when feeling well. High cholesterol has no symptoms, so the medication is still working even if you don't "feel" a difference.

Side effects to report:

• Mild GI symptoms (diarrhea, stomach pain, gas) are common and often resolve
• Report unexplained muscle pain, tenderness, or weakness promptly, especially if also taking a statin
• Report signs of liver problems: yellowing of skin or eyes, dark urine, persistent nausea, or unusual fatigue

Medication safety:

• Tell your healthcare provider about all medications, supplements, and herbal products you're taking
• Do not start new medications without checking for interactions first

Follow-up:

• Keep all scheduled lab appointments for lipid panels and liver function monitoring
• Bring up any new symptoms or concerns at each visit