The painkiller Bextra could pose an even greater risk of heart attack or stroke than Vioxx, according to a Pennsylvania scientist.

That scientist, Garret A. Fitzgerald, made the statement at a conference of the American Heart Association earlier this month. He said heart attacks and strokes occurred twice as often among patients in his study using Bextra as among those using placebos. Bextra is designed to treat joint pain, inflammation and stiffness associated with illnesses such as arthritis.

However, Fitzgerald warned against “overstating” the findings of his study, and Pfizer, the company that makes Bextra, pointed out in a news release that Fitzgerald’s findings were not published in a medical journal or subject to independent scientific review.

Pfizer officials said the Food and Drug Administration planned to convene an advisory committee in February 2005 to review the cardiovascular safety of all COX-2 inhibitors, the group of drugs that includes Bextra and Vioxx.

Merck, the maker of Vioxx, pulled the popular arthritis and pain medicine off the market worldwide in September after a study determined it could cause an increased risk of heart attack and stroke.

The problems with Vioxx showed up in some patients starting 18 months after receiving treatment with the drug, Merck officials said. Vioxx has been on the market in the United States since 1999 and was marketed in more than 80 countries.