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TUESDAY, April 20 (HealthDayNews) -- A popular arthritis medication appears to increase the risk of heart attack, but only in the first three months after starting the drug.

People taking Vioxx (generic name rofecoxib) had a 24 percent increased risk of heart attack compared with patients taking Celebrex (celecoxib) or nonsteroidal anti-inflammatory drugs (NSAIDs), claims a study in the April 19 issue of Circulation.

A spokeswoman for Merck & Co., which makes Vioxx, was quick to point out that this study is not the definitive word on the subject.

"This is an observational analysis with limitations, and it really must be interpreted within the context of data we have for randomized controlled trials for Vioxx," said Mary Elizabeth Blake. "Data from two large controlled trials showed no difference in the rate of serious cardiovascular thrombotic events in patients taking Vioxx vs. patients taking a placebo."

Another study, however, did show a higher rate of cardiovascular problems in patients taking 50 milligrams of Vioxx.

The study author also agreed this data is not sufficient reason to discontinue taking the medication. "When looking at the selective cox-2 inhibitors or looking at NSAIDs in general, it's very important to weigh the potential risks against the potential benefits," said study author Dr. Daniel Solomon, an associate physician at Brigham and Women's Hospital in Boston. "These drugs have a benefit. We need to understand which patient groups are the groups that receive the most benefit."

Nevertheless, Solomon pointed out, more than 41 million prescriptions for coxibs (another name for cox-2 inhibitors, the class of medication to which Vioxx and Celebrex belong) were filled in 2000, which makes any adverse health effects a potential public health problem. People suffering from osteoarthritis commonly take coxibs because they do not carry the same risk of stomach ulcers and intestinal bleeding as NSAIDs such as ibuprofen.

The study authors looked at 54,475 patients aged 65 years or older who were treated with a coxib, a traditional NSAID or neither. Individuals taking Vioxx had a 24 percent increase in heart attack risk compared with individuals taking Celebrex, who did not have an increased risk. The risk appeared to be highest in those taking more than 25 milligrams of Vioxx daily during the first 60 days of use.

Participants taking Vioxx had a 17 percent higher risk of heart attack compared with those taking NSAIDs such as Motrin and a 14 percent higher risk than patients not taking anti-inflammatory medications.

Solomon said he was not surprised by the findings. "It's very consistent with the findings from the VIGOR trial, which was a randomized trial which found a fourfold increase in heart attacks," he stated.

As to why the risk was elevated in the first 90 days, Solomon said, "I can't answer that with any level of certainty."

A potential explanation, he added, was that people who are susceptible to side effects are going to have them early.

It is also unclear what biological mechanism might explain why one cox-2 inhibitor had different side effects than another.

"They're different molecules, different structure. And we know from looking at drug epidemiology of other medications and other conditions that oftentimes one drug in a class may behave slightly differently than other members," Solomon said. "Exactly what it's doing in the body's biology and why one would have an increased risk of heart attack is not entirely clear."

Blake felt that study biases were a more likely explanation. "In this study, hormone therapy was associated with a reduced risk," she pointed out. In fact, the Women's Health Initiative has shown that hormone therapy is not associated with a reduced risk of cardiovascular disease.

More information

Learn more about osteoarthritis and drug treatments at the Arthritis Foundation.

(SOURCES: Daniel Solomon, M.D., associate physician, Brigham and Women's Hospital, and assistant professor, medicine, Harvard Medical School, Boston; Mary Elizabeth Blake, spokeswoman, Merck & Co., Inc., Upper Gwynedd, Pa.; April 19, 2004, Circulation)

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