Enlarge Bloomberg News A new study, the second in as many years, found that a prescription version of the drug niacin reduced artery plaque much better in eight months than ezetimibe, the active ingredient in Vytorin and Zetia. Merck Research Laboraties, which makes ezetimibe, questions the limitations of the new study, which was small in size and stopped early. ORLANDO  The blockbuster cholesterol drugs Vytorin and Zetia suffered a major setback Sunday when doctors released the results of a second study in as many years that raises concerns about how well the drugs work. The new study found that a prescription version of the drug niacin, used in different forms for half a century, reduced artery plaque significantly better in eight months than ezetimibe, the active ingredient in both Vytorin and Zetia. Patients in the ezetimibe group also suffered more heart attacks and other major heart problems than those in the niacin group, but the numbers were too small to draw conclusions, says the lead author, Allen Taylor, of the Washington (D.C.) Hospital Center. Q&A: What you should know about Vytorin, Zetia "The question is whether ezetimibe works at all," Taylor says. "Niacin has been around for 50 years. It's a well-understood drug, and in this trial it was a clear superior choice." Taylor acknowledged that the study has limitations, particularly its small size, and the fact that it was stopped after 14 months because patients in the niacin group were doing better. Peter Kim, president of Merck Research Laboratories, ezetimibe's maker, seized on the limitations to defend the drug. "It would be very unfortunate if a flawed scientific analysis led patients to discontinue their cholesterol treatment," Kim said. The findings, released Sunday at an American Heart Association meeting and published online by the New England Journal of Medicine, come about a year after a previous study showed that Vytorin, a combination of ezetimibe and cholesterol-lowering simvastatin, worked no better than simvastatin alone. Taken together, the studies dealt a body blow to a pair of drugs with sales of roughly $21 billion worldwide since 2003, Securities and Exchange Commission documents show. Vytorin and Zetia should be used for patients who can't adequately reduce their cholesterol with statins and niacin, says Roger Blumenthal, director of preventive cardiology at Johns Hopkins Cardiovascular Institute and author of an editorial detailing the limitations of the study. The other drug used in the study was Niaspan, made by Abbott Laboratories, a slow-release form of niacin. Niacin's side effects of itching and flushing make it difficult for patients to tolerate, says Ralph Brindis of Kaiser Permanente in Oakland. The study, sponsored by Abbott, involved 363 people who had heart disease or a high risk of heart problems. All had been taking statins and had relatively low levels of bad cholesterol. Half of the patients were given Niaspan, and half were given Zetia. Ultrasound images of neck arteries showed that Niaspan reduced artery plaque by 2%; Zetia did not. Two people in the Niaspan group had heart attacks or other major cardiac events, vs. nine in the Zetia group. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more