Merck disputed the findings of the study, and the name of a company epidemiologist who had worked on it was removed from the report before it was published in a medical journal.
In those studies, researchers did not see a similar increase in risk from Celebrex, another COX-2 inhibitor, which is made by Pfizer.
In August, Kaiser Permanente, a large nonprofit health maintenance organization, said that a review of its patient records indicated that those taking Vioxx on dosages greater than 25 milligrams faced a threefold increased risk of heart attacks and cardiovascular problems. An FDA official worked on that report.
Merck officials have long said that the earlier studies, like the Kaiser one, were not definitive because they were surveys based on patient records, rather than a clinical trial in which a drug's effectiveness and side effects are measured against a placebo in real time.
But last week, Merck received bad news from researchers in just such a trial.
The test, carefully designed to show if Vioxx was more effective than a placebo in preventing potentially cancerous colon polyps, found, instead, that the drug increased the risk of heart attack and strokes.
Janet Skidmore, a spokeswoman for Merck, said Thursday that the colon cancer study was the first clinical trial to show such results and the company took immediate action upon receiving data.
But Dr. David Campen, the medical director for drug information, utilization and medical information at Kaiser, said he thought the results of the colon cancer trial were simply another brick in the mounting body of evidence against Vioxx.
"I think they made a decision that it was just too risky for them to keep marketing the medication," he said.
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