While Merck battles thousands of people in courtrooms across the United States who claim its arthritis pain drug, Vioxx, caused strokes and heart attacks, Pfizer has continued to sell its similar drug, Celebrex. But Pfizer’s good fortune may be about to run out.

A new study in the March issue of the Journal of the Royal Society of Medicine concludes that Celebrex has cardiovascular side effects “similar in magnitude” to those of Vioxx, and should not be given preferential treatment by regulators. Vioxx was pulled from the market in 2004, when trials showed it caused an increased risk of heart attack and stroke in some patients.

Journal of the Royal Society of Medicine

The study is significant because Celebrex falls into a class of painkillers called COX-2 inhibitors. Three such compounds have been approved by the U.S. Food and Drug Administration, with two—Merck’s Vioxx and Pfizer’s Bextra—since pulled from the market because of safety concerns.

Celebrex stayed on the market, with the FDA’s strongest safety warning added to its label.

The paper’s authors argue that “the preferential risk/benefit assessment afforded [Celebrex] over other COX-2 inhibitors by the FDA may not be supported by the currently available evidence.” According to the paper, Celebrex raised the risk of heart attack 1.88 times compared to all comparator groups. Vioxx increased it 2.24 times.

To conduct the study, Brent Caldwell, a medical research fellow at the Medical Research Institute of New Zealand in Wellington, used a meta-analysis—an approach considered by many scientists to provide a more holistic conclusion than a single study because it compiles data from many clinical trials—to test the safetyof Celebrex.

Pfizer spokesperson Shreya Prudlo criticizes the paper and claims the studies included in the meta-analysis were only compared to a placebo. “Arthritis patients need medication and are already confused about their treatment options,” she says.

Although Celebrex has so far remained on the market, safety concerns significantly dented sales from $3.3 billion in 2004 to $1.78 billion in 2005. And much like Merck, Pfizer is now facing litigation over the side effects of its COX-2 drugs. An American woman who tookCelebrex and had a stroke in 2005 will try to sue Pfizer in an Alabama court in June.

Whether the meta-analysis has any influence on Celebrex’place on the market has yet to be seen. Recently, the cardiovascular safety of even the most common over-the-counter painkillers, such as Advil and Motrin, has been called into question. A paper in the British Medical Journal in June 2005 reported one in every 1,005 patients over the age of 65 taking ibuprofen was likely to suffer a first-time heart attack. Compared to the heart attack risk for Vioxx, which the same study put at one in 695, ibuprofen doesn’t look a whole lot safer.