21.3 Bile Acid Sequestrants, Fibrates, and Niacin

Bile Acid Sequestrants, Fibrates, and Niacin

Statins are the first-line drugs for lowering lipids, but they don't work alone for every patient. Bile acid sequestrants, fibrates, and niacin each target different parts of lipid metabolism, making them useful as alternatives or add-on therapies. Understanding how they differ in mechanism, side effects, and nursing considerations is essential for safe administration.

Overview of the Three Drug Classes

Bile acid sequestrants (cholestyramine, colestipol, colesevelam) bind to bile acids in the intestine and prevent their reabsorption. Their primary effect is lowering LDL cholesterol.

Fibrates (gemfibrozil, fenofibrate) activate peroxisome proliferator-activated receptor alpha (PPAR-α), a nuclear receptor that regulates lipid metabolism. Their primary effect is lowering triglycerides, with a secondary benefit of raising HDL cholesterol.

Niacin (vitamin B3, also called nicotinic acid) inhibits the synthesis and release of VLDL from the liver. It's the most versatile of the three: it lowers LDL, lowers triglycerides, and raises HDL.

How Each Drug Class Reduces Lipid Levels

Bile Acid Sequestrants

Bile acids are made from cholesterol in the liver and released into the intestine to help digest fats. Normally, most bile acids get reabsorbed and recycled. Bile acid sequestrants break that cycle:

1. The drug binds bile acids in the intestine, forming an insoluble complex.
2. That complex is excreted in the feces instead of being reabsorbed.
3. The liver compensates by pulling more cholesterol from the blood to make new bile acids.
4. Blood LDL cholesterol levels drop as a result.

Fibrates

Fibrates work through the PPAR-α receptor to shift lipid metabolism in several ways:

1. They increase lipoprotein lipase activity, which breaks down triglyceride-rich lipoproteins (like VLDL) in the bloodstream.
2. They reduce hepatic VLDL production.
3. They enhance removal of LDL particles from the blood.

The net effect is a significant drop in triglycerides and a modest increase in HDL.

Niacin

Niacin acts on multiple targets, which is why it affects the full lipid panel:

1. It inhibits the liver enzyme responsible for triglyceride and VLDL synthesis, so less VLDL is released into the blood.
2. Less VLDL means less LDL is formed downstream (since VLDL is eventually converted to LDL).
3. It increases lipoprotein lipase activity, enhancing breakdown of triglyceride-rich lipoproteins.
4. It reduces HDL catabolism (breakdown), so HDL levels rise.

Side Effects and Drug Interactions

A few things to highlight:

• The flushing with niacin is prostaglandin-mediated and typically affects the face and upper body. It's the most common reason patients want to stop the drug.
• Both fibrates and niacin raise myopathy risk when paired with statins. If a patient is on a combination regimen, muscle complaints should always be taken seriously.
• Bile acid sequestrants don't enter the bloodstream, so their systemic side effects are minimal. The main concern is their interference with absorption of other drugs.

Nursing Considerations

Bile Acid Sequestrants

• Administer with plenty of fluids to reduce GI side effects (the powder forms especially need to be mixed well).
• Separate from other medications by at least 1 to 2 hours (give other drugs 1 hour before or 4 to 6 hours after the sequestrant). This is critical because sequestrants can bind other drugs in the gut and block their absorption.
• Monitor for constipation. Recommend a high-fiber diet and adequate hydration.

Fibrates

• Assess for signs of myopathy: muscle pain, tenderness, or weakness, especially if the patient is also taking a statin.
• Monitor liver function tests (LFTs) periodically, as fibrates can cause hepatotoxicity.
• Instruct patients to report muscle pain, weakness, or dark-colored urine (a sign of rhabdomyolysis) immediately.

Niacin

• Administer with food to reduce both flushing and GI upset.
• Titrate the dose gradually. Starting at a low dose and increasing slowly helps the body adjust and reduces flushing severity.
• Pre-treat flushing with aspirin or an NSAID taken 30 minutes before the niacin dose. Advise patients to avoid hot beverages and alcohol around dosing time, as these worsen flushing.
• Monitor blood glucose and uric acid levels regularly. Niacin can worsen hyperglycemia in diabetic patients and precipitate gout in those with elevated uric acid.

Patient Education

For patients on bile acid sequestrants:

• Explain that the drug works by trapping bile acids in the gut, which forces the liver to use up cholesterol. This is why LDL goes down.
• Stress the importance of taking other medications at least 1 to 2 hours apart from the sequestrant so those drugs are properly absorbed.
• Provide practical constipation management: increase dietary fiber, drink plenty of water, and stay physically active.

For patients on fibrates:

• Explain that the drug primarily targets triglycerides and can also raise HDL.
• Tell patients to report any unexplained muscle pain, weakness, or dark urine right away. This is especially important if they're also on a statin.
• Reinforce the need for regular follow-up labs (LFTs and lipid panels).

For patients on niacin:

• Explain that niacin improves the entire lipid profile: it lowers LDL and triglycerides while raising HDL.
• Prepare patients for flushing. Let them know it's common, usually temporary, and tends to improve over time as the body adjusts. Taking aspirin 30 minutes beforehand and avoiding hot drinks or alcohol around dosing time can help.
• Advise patients to report persistent side effects or worsening of pre-existing conditions like diabetes or gout.
• Emphasize the importance of regular monitoring of glucose and uric acid levels.