A Merck & Co. official said Wednesday that all painkillers in the same class as the company's Vioxx (search) may cause heart problems or strokes, a change from the drug-maker's earlier position that such health issues appeared limited to its drug.

Dr. Ned S. Braunstein, senior director of Merck Research Laboratories, told two panels of Food and Drug Administration advisers that since the company pulled Vioxx from the market last year, studies suggesting similar problems with Celebrex (search) and Bextra (search) have changed his mind.

"The data strongly suggest it is a class effect," for all drugs of that type, Braunstein said.

The drugs, designed to help people in chronic pain from conditions such as arthritis (search), are known as Cox-2 inhibitors. At least two other Cox-2 drugs are awaiting approval from the FDA, Arcoxia from Merck and Lumiracoxib from Novartis Pharmaceuticals.

The panels plan to discuss those drugs Thursday.

The two advisory committees are holding a joint three-day session to gather data on the safety of Cox-2 drugs and to make recommendations regarding their future use.

Recommendations could range from limiting these drugs to people not known to be at risk of heart problems, reducing the dose or duration of use, requiring tougher warning labels and even taking the drugs off the market.

Merck pulled Vioxx off the market Sept. 30 after a long-term study showed a higher rate of strokes and heart problems in people using the drug.

A panel of federal judges on Wednesday assigned all pending Vioxx product liability lawsuits against Merck to Judge Eldon E. Fallon in Louisiana, who is experienced in major pharmaceutical litigation.

An FDA health official told the panels there were preliminary indications of heart problems with Vioxx before it was withdrawn, but it was difficult to sort through conflicting data.

"We were not asleep at the wheel, we were actually engaged in reviewing a lot of data," Dr. Lourdes Villalba told a joint meeting of the Food and Drug Administration's arthritis advisory committee and its drug safety and risk management advisory committee, which are looking into Vioxx, Celebrex and Bextra.

Celebrex and Bextra, made by Pfizer Inc., remain on the market, though some studies have also indicated they, too, may carry an added heart risk.

Villalba, medical officer responsible for Vioxx at the FDA's Center for Drug Evaluation and Research, pointed out that a study done in 2000 comparing Vioxx with the painkiller naproxen, showed a higher rate of heart problems with Vioxx, but other studies had conflicting results. In discussions with Merck officials, she said, the company suggested naproxen might have a heart protective effect.

Nonetheless, in 2002 the agency required an added warning on the Vioxx label urging caution in prescribing it for people with heart conditions.

"We never bought the naproxen theory," she said.

But Merck officials still believe naproxen can help protect the heart, said Merck spokesman Christopher Loder.

Pfizer vice president Dr. Joseph M. Feczko said the reports of increased heart problems need to be seen in context, considering that the Cox-2 inhibitors bring an important benefit by reducing the sometimes serious stomach and intestinal problems that occur with many painkillers.

Dr. Kenneth M. Verberg, Pfizer vice president for inflammation and immunology, defended Celebrex as safe, though he said there is little data on use of the drug for more than one year. Further long-term testing of Celebrex is needed, he said.

Earlier, Braunstein, senior director of Merck Research Laboratories, reported that the biggest increase in heart problems occurred after 18 months of use.

Also earlier in the day, Dr. Garrett FitzGerald of the Department of Pharmacology at the University of Pennsylvania School of Medicine told the committees that, considering the hazard reports, similar new drugs may have to face tougher testing to win approval and those on the market ought to be put through the same new testing to retain approval.

FitzGerald told the panels that, just as low-dose aspirin affords heart protection and a small but definite risk of stomach and intestinal problems, so the Cox-2 inhibitors "afford gastrointestinal protection and a small but absolute risk of cardiovascular events."

As the session began, the FDA promised prompt action on recommendations from advisory committees.

Dr. Steven Galson, acting director of FDA's Center for Drug Evaluation and Research, reminded the committees that the drugs in question are important painkillers widely used by people in chronic pain. It is important to balance the risks of drugs with their benefits, he said.

A drug that has a positive risk-benefit balance for the population as a whole, Galson added, may still cause serious problems for some individuals.

The FDA has been criticized for being slow to recognize problems with these drugs.

However, committee chairman Dr. Alistair J. Wood of Vanderbilt University stressed as he opened the session that the panel "is not here to delegate blame or revisit the past."

On Tuesday, the Health and Human Services Department announced that the FDA will establish a new Drug Safety Oversight Board to monitor medicines once they're on the market and will update physicians and patients with emerging information on risks and benefits.