Dec. 17 (Bloomberg) -- Pfizer Inc. said its painkiller Celebrex, which is in the same class of drugs as Merck & Co.'s withdrawn Vioxx, increased the risk of heart attacks in a study. Pfizer shares plunged as much as 24 percent, wiping out about $41 billion in market value.

Patients in a U.S. National Cancer Institute study taking 400- milligram and 800-milligram doses of Celebrex daily had a 2.5 fold increase in their risk of a cardiovascular event compared with those on placebo, Pfizer said in a statement today. The institute suspended dosing of Celebrex in the study.

Regulators in the U.S. and Europe already are taking a closer look at the Cox-2 class of painkillers after Merck pulled Vioxx off the market Sept. 30 in the biggest withdrawal ever of a prescription drug. Pfizer Chief Executive Officer Hank McKinnell said as recently as Dec. 6 that there was no evidence Celebrex was dangerous. More than 27 million people in the U.S. have been prescribed Celebrex since its introduction in 1999.

``It's going to bring up the same issues as Merck with Vioxx, litigation risk and all the rest,'' said Sena Lund, an analyst with Cathay Financial in New York, who has an ``outperform'' on shares of New York-based Pfizer and owns them. ``It's definitely not positive for the company, especially if they have to pull the drug.''

No Plans to Withdraw

Pfizer officials couldn't immediately comment on details of the study beyond the information contained in the release, said Paul Fitzhenry, a company spokesman.

``Pfizer has no plans to withdraw Celebrex from market,'' Fitzhenry said.

The U.S. Food and Drug Administration and cancer institute also declined to comment immediately.

Pfizer, the world's biggest drugmaker, said the negative finding from the NCI study was unexpected and inconsistent with other research. Pfizer shares fell $4.17, or 14 percent, to $24.81 at 11:37 a.m. in New York Stock Exchange composite trading, after dropping to $21.99. The decline was the biggest in at least two decades.

Public Citizen, a consumer group that monitors the FDA, has been preparing a petition asking the FDA to take Celebrex and Pfizer's Bextra, which is in the same class of drugs, off the market.

``They should come off the market and our petition will be filed in the next several weeks to ban both of these drugs,'' said Sidney Wolfe, the director of the Washington-based organization's Health Research Group.

Congress Examining

The Vioxx withdrawal has prompted Congress to examine how the FDA monitors the risks of medicines. The Senate Finance Committee held a Nov. 18 hearing where FDA reviewer David Graham said the agency is incapable of protecting the U.S. against another drug with risks such as Vioxx.

Senate Finance Committee Chairman Charles Grassley intends to introduce legislation to make the FDA's Office of Drug Safety more independent. The committee oversees U.S. government health- insurance programs that pay for drugs, giving it a stake in the FDA's performance, Grassley said in November.

The House Energy & Commerce Committee, which oversees FDA, also have said they are scrutinizing the agency's performance.

Vioxx and Celebrex were supposed to be gentler on the stomach because they targeted the Cox-2 enzyme that is involved with pain. Older painkillers can cause stomach irritation by interfering with Cox-1, a related enzyme.

That difference was intended to justify the cost, sometimes more than $2 a pill, of these drugs, while generic painkillers sell for pennies each. Neither Merck nor Pfizer was able to prove that their painkillers were substantially different from older medicines, Wolfe said.

The Study

``The market sees a much larger risk today, not only about products in the pipeline but also products already on the market,'' said Stefan Ingildsen of BankInvest in Copenhagen, which manages about $9 billion and holds share of Pfizer. ``There's very little incentive to invest in this sector at all at the moment.''

The U.S. National Cancer Institute has been studying whether Celebrex might aid in preventing growths known as polyps that put people at risk for colon cancer. The heart risk findings were discovered during one of the trials. Another study, also intended to see if Celebrex can prevent some growths, found no increased heart risk for patients taking a 400-milligram dose of Celebrex compared with a group taking placebo, Pfizer said.

Celebrex is approved for use in the U.S. for the treatment of arthritis and pain, at recommended doses of 100 milligrams to 200 milligrams daily for osteoarthritis, and 200 milligrams to 400 milligrams a day for rheumatoid arthritis.

The FDA plans to hold an advisory committee meeting next year to review the safety of the Cox-2 painkillers.

Bextra

Pfizer has already disclosed that its other Cox 2 painkiller, Bextra, is linked to an elevated risk of blood clots and heart attacks and strokes in cardiac surgery patients. The company on Dec. 9 said it would warn doctors of that risk. Bextra was one of five drugs that FDA reviewer Graham identified as unsafe at a Nov. 18 U.S. Senate hearing.

McKinnell said in an interview Dec. 6 that even if Bextra was found to have cardiovascular risks, he might not withdraw the drug.

``In the case of Bextra, I'm not sure that would be the right answer,'' he said in the interview. ``A better approach may in fact be label for the known risks and let the physician decide what is the best drug for you given your personal circumstances.''

Pfizer bonds weakened compared with government securities, as investors demanded a bigger yield premium to buy the debt. The so-called spread on the company's 4.5 percent notes maturing in 2014 widened about 7 basis points to about 45 basis points, traders said. A basis point is 0.01 percentage point.

To contact the reporter on this story: Kerry Dooley in Washington at kdooley@bloomberg.net.

Last Updated: December 17, 2004 11:48 EST