News that the popular cholesterol drug Vytorin may not work to protect arteries and may in fact worsen clogging should not cause patients to panic, the American College of Cardiology said.

They said the study -- which was carried on newspaper front pages and which depressed the shares of one of the makers, Schering-Plough -- was not the last word on the drug's efficacy.

Merck & Co and Schering-Plough said on Monday that in a study known as ENHANCE, Vytorin failed to significantly halt clogging of arteries better than an older generic drug.

Members of Congress said they planned to investigate the companies' handling of the study results, which were delayed for what many people considered to be a suspiciously long time.

In the meantime, patients should not suddenly stop taking the drug, the cardiology group said.

"There is no reason for patients to panic," the ACC said in a statement. "This is not an urgent situation and patients should never stop taking any prescribed medications without first discussing the issue with their health care professional," the statement added.

Vytorin combines two cholesterol-lowering drugs -- ezetimibe, sold under the brand name Zetia, and simvastatin, sold generically and under the Zocor brand name.

The study involved 720 patients with very high levels of cholesterol from an inherited form of heart disease. Doctors made images of their arteries to see if the drugs slowed the buildup of plaque, but the results showed that Zocor alone in fact worked better than Vytorin.

"According to the American College of Cardiology, this study deserves serious thought and follow-up," the group said.

"The overall incidence rates of cardiac events were nearly identical between both treatment groups, and both medicines were generally well tolerated."    

It said more studies to be published later would shed more light on the matter. Michigan Democratic Reps. John Dingell, chairman of the Committee on Energy and Commerce, and Bart Stupak, chairman of the Subcommittee on Oversight and Investigations, said they were investigating the way Merck and Schering-Plough handled the study.

"Additionally, Merck and Schering-Plough's delay in releasing study results, as well as their attempt to manipulate the data is, quite frankly, suspicious," Dingell said in a statement.

 "American consumers and their doctors should not have had to wait nearly two years for this information. Why did Merck and Schering-Plough go to great lengths to delay the study results? Why did they attempt to manipulate the data? We will continue our investigation until these questions are answered." - Reuters