Pfizer Incorporated, the world’s biggest drug maker, suspended sales of the Bextra painkiller at the request of American regulators and agreed to apply the government’s strictest warnings to its similar Celebrex drug.

The moves come six months after Merck & Company withdrew its related pain drug Vioxx because a company study linked it to an elevated risk of heart attacks and strokes. Bextra, which was also tied to a rare, fatal skin disorder, generated $1.29 billion, or 2.4%, of New York-based Pfizer’s revenue last year. Celebrex brought in $3.3 billion, or 6.3%.

The Food and Drug Administration went against advice from a panel of doctors and scientists at a February hearing that Bextra’s benefits outweighed its risks and should remain on the market. Pfizer said it disagreed with the FDA’s finding that Bextra should be withdrawn.

“It would have been easy for the FDA to say, ‘We’re following the advice from the advisory committee,'” and to permit Bextra sales to continue, said an epidemiologist at Wake Forest University in Winston-Salem, N.C., who was a member of the FDA panel, Curt Furberg. “But they went against Pfizer. Pfizer was against pulling the drug but had to agree.”

The FDA also said older, nonprescription painkillers such as ibuprofen and naproxen will have to carry cautions on risks of heart attacks and stomach bleeding. Aspirin won’t have such a warning because it has been shown to protect against heart attacks, the agency said.

After the Vioxx recall, the biggest drug withdrawal in history, the acting FDA commissioner, Lester Crawford, 67, was called before congressional panels a record four times in a single week to answer questions about whether the agency should have done more to protect consumers from risks linked to Vioxx and to prevent a shortage of influenza vaccine.

Yesterday’s action is “a sign the FDA is getting more proactive,” said Rodolphe Besserve, an analyst at Kepler Equities in Paris. “It’s bad for the whole market. I see more restrictions on labeling, and we can’t exclude that some other products will be the subject of the FDA’s attention.”

Health and Human Services Secretary Michael Leavitt announced in February that the FDA would set up a board to monitor the safety of prescription drugs. The agency regulates more than $1.5 trillion in drugs, devices, and other products.

Pfizer’s chief executive, Hank McKinnell, 62, was quick and persistent in defending the company’s pain drugs after the Vioxx withdrawal. Bextra was linked to an elevated risk of blood clots, heart attacks, and strokes in cardiac-surgery patients, resulting in the December 9 addition of a safety warning to its label. The company disclosed December 17 that a study linked Celebrex to elevated heart risks.

Since then, new prescriptions for Celebrex have fallen about 58%, according to data provided by Yardley, Pa.-based Verispan, which tracks more than 50% of all American pharmacy prescriptions. Celebrex was the world’s best-selling arthritis medication last year.

New Bextra prescriptions have dropped more than 80% since the beginning of October. More than 27 million people in America have been prescribed Celebrex since 1999, and more than 7 million have used Bextra worldwide since 2002.

The resulting plunge in revenue contributed to a restructuring that Mr. McKinnell announced three days ago. Pfizer said earnings will fall 25% this year as sales growth stalls and the company invests in a program aimed at cutting $4 billion in costs. In addition to lost sales of Celebrex, Mr. McKinnell faces the expiration of patents on drugs that account for almost a third of revenue.

Pfizer must add a warning highlighted in a black box to the label of Celebrex. The FDA said the caution would include increased risk of “cardiovascular events and gastrointestinal bleeding.” Celebrex, Bextra and Vioxx are part of a class of drugs designed to target the body’s production of the Cox-2 enzyme, linked to pain and swelling, while sparing a related enzyme that helps protect the stomach.

“Celebrex should only be used in a very, very small number of patients,” said Alastair Wood, a professor of medicine and pharmacology at Vanderbilt University in Nashville, Tennessee, who was chairman of the FDA advisory panel on pain drugs.

Pfizer said it will hold talks with the agency about returning Bextra to the market. Patients should stop taking Bextra and contact their doctors, Pfizer said.