The newly released results of a preliminary study suggest that the drug Vytorin, which combines the cholesterol-lowering drug ezetimibe with a statin, may slow the growth of arterial plaque no more effectively than a statin taken alone.
Because ezetimibe lowers cholesterol by a different mechanism than statins, it was hoped that a combination of the two drugs would be more effective than either drug used alone. But it was not.
Arterial plaque is what raises the risk of heart attack and stroke. The trial, called the ENHANCE study, followed 720 people with a gene that causes very high LDL, or “bad,” cholesterol levels. For two years, half of the participants were assigned to receive Vytorin containing ezetimibe and the statin drug simvastatin (brand name Zocor; also available generically). (Ezetimibe is also sold separately under the brand name Zetia). The other half received simvastatin alone.
The combination of drugs did lower LDL cholesterol levels more than the statin alone. Over the course of the study, the people who took only simvastatin had an average reduction in their LDL cholesterol levels of 41%. The people who took simvastatin combined with ezetimibe had a greater reduction in their LDL cholesterol levels—58%. But there was no significant difference in the growth of plaque in people who took the combination of the two drugs and in those who took simvastatin alone. According to the American Heart Association, the study was not large or long enough to determine whether the drug combination was more or less effective than simvastatin alone in decreasing heart attacks or deaths.
This study was funded by Merck and Schering-Plough, the companies that manufacture Zetia and Vytorin. There has been some controversy over the release of results from the study, because the trial ended in April 2006 and findings were originally scheduled for publication in early 2007. However, the companies put off publishing the results, claiming they were continuing to analyze data from the trial.
According to The New York Times, Zetia and Vytorin currently account for about 20% of the cholesterol-lowering market in the United States, and 100 million prescriptions for the two drugs have been filled since they were approved by the U.S. Food and Drug Administration (FDA). Zetia was approved in 2002 and Vytorin was approved in 2004.
The ENHANCE study has not challenged earlier findings that showed ezetimibe to be effective at lowering cholesterol levels. However, other research has indicated that statin drugs may have positive effects on heart health above and beyond their cholesterol-lowering functions. Because ezetimibe lowers cholesterol in a different way than statins do—ezetimibe blocks intestinal absorption of dietary cholesterol, while statins block the action of an enzyme in the liver that controls the production of cholesterol—the newer drug may not have the same positive effects. And because it is not available generically, it is more expensive than many generic statin drugs.
The full results of the ENHANCE study will be presented at the American College of Cardiology meeting in March and subsequently published in a major medical journal. Meanwhile, larger trials of ezetimibe involving other types of high-risk participants are under way. Results from these trials should be available over the next few years.
The American College of Cardiology (ACC) “recommends that major clinical decisions not be made on the basis of the ENHANCE study alone,” and Daniel W. Jones, M.D., President of the American Heart Association (AHA), pointed out that “Vytorin does not appear to be unsafe” and said that “we do not believe patients should stop taking the drug on their own.” (The AHA receives funding from Vytorin’s manufacturers and the ACC also receives money from the drug industry.)
People who take ezetimibe, either alone or in combination with simvastatin, and are concerned over these study findings should talk to their doctors about what cholesterol-lowering treatment is best for them.