Pfizer Inc. (PFE) said Monday it plans a major study to see if its pain medication Celebrex (search) can help osteoarthritis patients at risk for cardiovascular disease.

The announcement comes almost three weeks after Merck & Co. (MRK) pulled Vioxx (search), its rival drug that is also a COX-2 inhibitor, from the market because it doubled the risk of heart attack and strokes in patients taking the medication longer than 18 months.

And just last week, Pfizer said a study showed that Bextra, another COX-2 inhibitor (search) it sells, increased the risk of heart attacks in patients that had coronary bypass operations. Pfizer shares closed down 2 percent on Friday to $28.50.

In a statement, Pfizer said that in completed studies and ongoing trials Celebrex has proven to be safe and also has shown it could help patients with cardiovascular disease.

The study, which is expected to begin next year, will enroll more than 4,000 patients around the world who have osteoarthritis and had a recent heart attack.

Pfizer shares were up 20 cents to $28.70 on Monday on the New York Stock Exchange