Dec. 20 (Bloomberg) -- The U.S. National Institutes of Health halted an Alzheimer's prevention study of Pfizer Inc.'s Celebrex painkiller and the generic naproxen drug because of a heart risk.

Patients taking naproxen, which belongs to a class of medicines called nonsteroidal anti-inflammatory drugs, had a higher rate of heart attacks than those given a placebo. Celebrex did not increase the risk of heart disease in the 2,400 patient- study, NIH officials said in a conference call.

NIH researchers said they were concerned about Celebrex after Pfizer released results from a separate study on Dec. 17 that found higher doses of Celebrex more than doubled the risk of heart attacks. Doctors at Brigham and Women's Hospital and Massachusetts General Hospital in Boston will make recommendations about Celebrex use tomorrow because of last week's findings.

``We have to ask that question: Is this a class phenomenon to all the nonsteroidal anti-inflammatory drugs?'' said Sandra Kweder, acting director for the office of new drugs at the U.S. Food and Drug Administration's Center for Drug Evaluation and Research.

Pfizer officials couldn't immediately comment on the report. Germany's Bayer AG sells naproxen as Aleve.

Bayer ``has not yet seen the data and is unable to comment on the study at this time,'' said William O'Donnell, a company spokesman. ``In the meantime, we are in agreement with the FDA's recommendation that consumers carefully follow the instructions'' for taking Aleve.

Recommended Dose

Patients taking naproxen shouldn't exceed the recommended dose and shouldn't take the medicine for more than 10 days, said the FDA's Steve Galson.

The National Institute on Aging is sponsoring the Alzheimer's research. Patients in that study were divided into three groups and received either a placebo, Celebrex or naproxen. Researchers will continue to monitor patients who participated in the study.

The NIH made the announcement after U.S. markets closed. Shares of Pfizer dropped $1.46, or 5.7 percent, to $24.29 at 4:02 p.m. in New York Stock Exchange composite trading. Pfizer's market value has plunged by $35 billion in the past two trading days.

A warning posted on New York's Hospital for Special Surgery's Web site recommends that Celebrex patients contact their physicians.

Contact Doctors

``Although we have not had the opportunity to see the actual data, we are concerned that this side effect occurred at a dose of Celebrex that is taken by many patients with arthritis,'' the hospital said in a message on its Web site. ``Until the data can be fully reviewed, we are recommending that patients who absolutely need this drug for control of arthritis contact their physicians.''

Pfizer Chief Executive Hank McKinnell said in an interview today with financial news network CNBC that Celebrex should remain on the market. The company's own studies have failed to turn up a heart risk, McKinnell said in the interview.

The company is planning studies next year that may show that Celebrex actually cut heart risk, McKinnell told CNBC. An FDA committee will review the drug in February, McKinnell said.

``I would hope we are not rushed to judgment before we are able to look at all the evidence,'' McKinnell told CNBC.

To contact the reporter on this story: Nicole Ostrow in New York at nostrow@bloomberg.net.

Last Updated: December 20, 2004 22:59 EST