Millions of Americans suffer from hyperlipidemia, a condition characterized by elevated levels of cholesterol and other lipids found in the bloodstream. Hyperlipidemia has been shown to increase the risk of heart disease, stroke and pancreatitis. In order to regulate the amount of lipids in the bloodstream, many patients take cholesterol-lowering medications in the drug class known as statins. One of the mostly widely used medications in this class of drugs is simvastatin, trade name Zocor. Simvastatin is extensively metabolized in the liver by a specific enzyme. Unfortunately, grapefruit and grapefruit juice contain bioflavonoids and other compounds that can inhibit these liver enzymes. As a result, simvastatin drug levels may rise, causing adverse and sometimes severe side effects. This interaction also exists for many of the other drugs classified as statins.
Myopathy and Rhabdomyolysis
Muscle pain and weakness are symptoms of myopathy that cause the greatest concern in patients who may have excessive levels of simvastatin in the body. In severe cases, muscle breakdown and cell death can lead to a condition known as rhabdomyolysis. According to the Zocor product package insert, the risk of rhabdomyolysis is dose dependent. In theory, this suggests that increased simvastatin levels correlates with an increased risk of muscle deterioration. Although the mechanism by which simvastatin causes muscle breakdown is not definitively known, it has been proposed that the drug inhibits the synthesis of proteins and enzymes vital to muscle cell health.
Kidney Failure
As muscle breaks down, the cells release myoglobin, which is normally eliminated by the kidneys. Increased myoglobin production places increased burden on the kidneys. In addition, myoglobin is toxic to kidney cells, and together with the increased burden of elimination, may lead to renal failure.
Liver Dysfunction
The increased levels of simvastatin can also place additional burden on the liver, which is primarily responsible for metabolism of the drug. Statin therapy has been known to cause a detectable elevation in liver enzymes that are released after liver cell death.
Drug Interactions
In addition to simvastatin, other drugs are metabolized by the liver enzyme CYP3A4. After grapefruit inhibition, increased simvastatin levels can compete with other drugs for the remaining viable enzymes. As a result, toxicity and adverse effects can occur with other medications that are being used at the same time as simvastatin.
References
- MyMediaPharm.com: Mechanism of Grapefruit Interactions
- Merck: Zocor Product Package Insert
- "The Journal of the American Medical Association"; Statin-Associated Myopathy; Paul D. Thompson, M.D., Priscilla Clarkson, Ph.D., Richard H. Karas, M.D., Ph.D.; April 2003
- Lab Tests Online: Myoglobin
