Pfizer Inc. on Thursday suspended sales of its arthritis drug Bextra on requests by U.S. and European regulators, who said the risks of potentially fatal side effects outweigh the benefits.

The U.S. Food and Drug Administration also asked Pfizer to include a black box warning - the strongest possible - for its painkiller Celebrex. Bextra and Celebrex are part of a class of drugs known as COX-2 inhibitors that also includes Merck & Co.‘s Vioxx, which was withdrawn last year due to increased risks of strokes and Heart attacks.

The FDA said it singled out Bextra for suspension because it gives no added advantage as a painkiller and can cause a potentially life-threatening skin condition called Stevens-Johnson syndrome, an allergic reaction that usually begins as a blistering of the mouth and lips and can spread to the rest of the body.

The agency also asked the makers of dozens of other prescription and non-prescription painkillers, including Motrin, Advil and Aleve, to strengthen warnings about possible heart risks and potentially life-threatening gastrointestinal bleeding. The new warnings do not apply to aspirin.

Motrin and Aleve are members of a class of drugs known as non-steroidal anti-inflammatory drugs, or NSAIDs. Bextra, Celebrex and Vioxx are selective NSAIDs designed to reduce the risk of gastrointestinal bleeding.

Pfizer, whose shares fell 2 percent in morning trading, said it disagrees with the regulatory decision on Bextra and will explore options with the FDA under which it might be allowed to resume sales of the drug.

The FDA’s decision is the latest in a long series of actions by companies, regulators, advisors, lawyers and consumers that began last September when Merck withdrew Vioxx after a clinical trial showed it doubled the risk of heart attack and stroke in patients who took it for more than 18 months.

The FDA in December had called on doctors to limit prescribing Celebrex and Bextra in light of evidence that they also may increase the risk of heart attack and stroke.

The FDA said it is now willing to “carefully review” any proposal by Merck to reintroduce Vioxx.

An advisory panel to the FDA in February had concluded that Vioxx, Bextra and Celebrex all posed some level of heart risk, but said that Vioxx was safe enough to return to the U.S. market and that all three drugs should carry black box warnings.

Sales of Pfizer’s COX-2 inhibitors have slowed since then and investors had already expected increased warnings on both drugs, with a possible withdrawal of Bextra.

Shares of Pfizer, which in December had hit a four-year low of $23.52, were down 36 cents at $26.51 in morning trade on the New York Stock Exchange.

“We continue to believe that Celebrex is a good drug for Pfizer and will help drive numbers, just not at the levels we would have hoped for 18 months ago,” said Jason Fox, an analyst at H&R Block Financial Advisors.

Bextra had sales in 2004 of $1.3 billion, while sales of Celebrex were $3.3 billion.

Pfizer’s cholesterol treatment Lipitor is the world’s best-selling drug, with sales in 2004 of $10.86 billion.