Safety and Efficacy of Statins and Fibrates
Statins: Safety and Efficacy
Statins and fibrates are major classes of lipid-lowering agents. This section details their safety profiles, contraindications, side effects, and drug-drug interactions.
Contraindications of Statins
Statins are contraindicated during pregnancy because cholesterol is essential for fetal growth. Statins are competitive inhibitors of HMG-CoA reductase, which lowers cholesterol synthesis in the liver.
Side Effects of Statins
The common side effects of statins include:
- Myalgia (muscle pain)
- Myopathies (muscle weakness)
- Rarely, myositis (muscle inflammation) or rhabdomyolysis (muscle breakdown)
Explanation of Myalgia and Myopathy
Statins are taken in an acid form and convert to a lactone form after absorption. Lactones are more potent inhibitors of complex III in the mitochondrial transport chain. Inhibition of complex III activity by the lactone form is thought to be responsible for statin-induced myopathy because reduced complex III activity is observed in patients suffering from this side effect.
Drug-Drug Interactions with Statins
Statins are metabolized through cytochrome P450 enzymes:
- Some statins are metabolized by CYP3A4.
- Some statins are metabolized by CYP2C9.
Statins are also substrates for permeability glycoprotein (P-glycoprotein).
Cytochrome P450 Enzymes
Most CYP450 enzymes are expressed in the liver, where cholesterol synthesis occurs. Most CYP450-mediated drug-drug interactions occur in the liver.
P-Glycoprotein
P-glycoprotein uses ATP to actively pump substrates across the membrane out of the cell. In hepatic tissues, P-glycoprotein promotes secretion into bile. In the gut, P-glycoprotein prevents or reduces oral absorption of drugs.
Statin Interactions
Statins can inhibit CYP450 enzymes, or other drugs can affect the activity and metabolism of statins by CYP450 enzymes. This can result in an increase in statin serum concentrations. Additionally, statins have been reported as substrates and inhibitors of P-glycoprotein.
These drug-drug interactions can alter levels of LDL reduction. Inhibition of CYP450 enzymes by other drugs can cause statins to build up, leading to enhanced muscle-related toxicities.
Specific Drug Interactions
Patients requiring cardiovascular drugs often take combination therapies with statins and other cardiovascular medications. It's important to consider how these drugs might interact and affect the metabolism of either category of drugs.
- Statins and Fibrates: Both are associated with a risk of muscle-related toxicity, so combination therapy can increase this risk. Avoid combining gemfibrozil with lovastatin, pravastatin, and simvastatin. Gemfibrozil doesn't interact with atorvastatin, pitavastatin, and rosuvastatin to the same extent because they are metabolized by different CYP450 enzymes. These combinations can be used if clinically indicated. Fenofibrate is preferred for statin-fibrate combinations because it shows reduced drug-drug interactions with statins.
- Statins and Calcium Channel Blockers: Some increases in statin levels are seen with amlodipine. Lovastatin and simvastatin doses should be kept low. Diltiazem or verapamil can be used with certain statins when the potential benefit outweighs the risk. In general, a non-CYP3A4 metabolized statin is preferred when these two calcium blockers are used.
- Atorvastatin and Digoxin: Be aware of potential adverse interactions when combining atorvastatin and digoxin (an antiarrhythmic agent).