The drug pairs Merck's Zetia, which lowers low-density lipoprotein (LDL or "bad cholesterol") with the generic version of Lipitor, the best-selling statin made by Pfizer that lost its patent protection in 2011.
Although the combination drug, to be called Liptruzet, was shown in a clinical trial to reduce LDL cholesterol more than patients who took Lipitor alone, the company said Liptruzet did not reduce patients' chances of developing heart disease.
"This is extremely surprising and disturbing," said Dr. Steven E. Nissen, chairman of the department of cardiovascular medicine at Cleveland Clinic.
Cardiologists have long questioned the value of Zetia and Vytorin which were on the market for a decade but did not show any reduction with regard to the risk of heart disease.
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A clinical trial of more than 18,000 patients is assessing whether Vytorin significantly reduces heart attacks, strokes and heart-related deaths and is expected to conclude in 2014.
In March, an independent monitoring board let the trial continue saying no significant safety concerns had come up.
Morgan Liscinsky, an FDA spokeswoman, said high levels of LDL cholesterol were a known risk factor for heart disease.
"Liptruzet is a combination of two currently marketed drugs that effectively lower elevated levels of LDL cholesterol," she said.
The FDA rejected Merck's application for the drug last year, and the company said more information had been asked for.
Merck said Liptruzet was a good option for patients who were not successful in lowering their bad cholesterol.
"A significant percentage of patients are unable to lower their LDL cholesterol to recommended levels despite treatment," said Dr. Peter H Jones, an adviser to Merck and an associate professor of medicine at Baylor College of Medicine.
Sales of Vytorin and Zetia have fallen since 2007, when they brought in a combined USD 5 billion, but they are still among Merck's top-selling drugs.