Some 2 million people worldwide are taking the drug, making Merck's move one of the largest prescription drug withdrawals in history. Since the arthritis medicine was introduced in 1999, roughly 84 million prescriptions have been written for it.
"We are taking this action because we believe it best serves the interests of patients," said Raymond Gilmartin, chairman and chief executive of Merck. "Given the availability of alternative therapies and the questions raised by the data, we concluded that a voluntary withdrawal is the responsible course to take."
Sales of Vioxx already had been deteriorating during the last two years following several observational studies and analysis of medical claims that showed the drug caused cardiovascular problems.
But Merck was not convinced. It stood by the product until Thursday, when it said it was able to view comparative data from a clinical trial of what it called a "broad base" of patients comparing their experience on the medication to those who took a placebo.
That trial, which looked at whether Vioxx could prevent some cancers, showed that the drug at a 25-milligram dose doubled the "risk of a cardiovascular event," the company said.
"Some of us in the medical profession have seen this coming and have been discussing this with patients," said Dr. Calvin Brown, an associate professor of rheumatology at Rush University Medical Center in Chicago. "I don't think Merck hid anything, but they saw the glass as half full but many of us in the medical profession saw it as half empty."
The stakes were high for Merck, which generated more than $2 billion a year in sales from a drug that has been among the top 20 medications in the U.S. in terms of sales.
Vioxx accounted for 11 percent of Merck's $22.5 billion in sales and was needed as the drugmaker faces the loss of patent protection for other top-sellers, such as the company's popular cholesterol drug Zocor, which could face generic competition in 2006.
On news of the product withdrawal, Merck shares plunged $12.07, or 27 percent, to $33 in heavy trading on the New York Stock Exchange.
Earnings to fall
Merck said the Vioxx move will trim 50 to 60 cents a share from its earnings for the rest of the year because of foregone sales, write-offs of inventory held by Merck, customer returns of product and related costs of the withdrawal.
"It's a disaster for Merck, coming at the worst time," health-care analyst Hemant Shah of HKS & Co. in Warren, N.J., told The Associated Press.
Vioxx had been part of a "super-aspirin" drug class known as cox-2 inhibitors, a group of medications hailed for longer-term use because they do not harm the lining of the stomach as do aspirin and ibuprofen, which are known as "non-steroidal anti-inflammatories."
The drug was primarily used to treat people suffering from osteoarthritis, a disease of the joints affecting more than 20 million Americans.
Given the latest news on Vioxx, at least one consumer group said patients should also stop using the two other most-prescribed cox-2 inhibitors, Celebrex and Bextra, which are sold by Pfizer Inc.
"Today's announcement by Merck is the latest evidence that this family of drugs, the cox-2 inhibitors, once referred to as `super-aspirins' are turning out to be more like super-disasters," said Dr. Sidney Wolfe, Director of Public Citizen's Health Research Group.
Drugs have defenders
But Pfizer and some doctors defended Celebrex and Bextra, saying available data and clinical studies have not shown problems similar to the cardiovascular issues with Vioxx.
"The cardiovascular data for Celebrex and Bextra in the long-term arthritis studies has been good," said Dr. Gail Cawkwell, Pfizer's worldwide medical director for Celebrex.
Celebrex, the nation's most widely prescribed cox-2, was developed by the former G.D. Searle & Co. of Skokie, which was part of Pfizer's purchase last year of Pharmacia Corp. Pfizer has since closed the Searle operation.
Merck's latest study covered three years and was the first study "of this length ever conducted with a cox-2 inhibitor," the New Jersey-based drugmaker said in a statement.
In the first 18 months of the study, Merck said, there was no difference in the risk of heart attack or stroke in patients taking Vioxx or a placebo. "Beginning after 18 months, however, the risk of cardiovascular event did increase among those on Vioxx," said Merck's Gilmartin.
In the three-year clinical trial of 2,600 patients, where half were on placebo and half on Vioxx, 3.5 percent of the Vioxx patients suffered a heart attack or stroke, while only 1.9 percent of the patients in the placebo group suffered a cardiovascular event, the FDA said.
The FDA said patients should stop taking the drug and schedule an appointment with their doctors to discuss what medication they should now take. "We agree with Merck's actions and believe they did the right thing," an FDA official said in a conference call Thursday.
Merck said the company believed it could have continued to market the drug by adding information to its warning label.
FDA officials declined to say whether they had been planning to force Merck to recall the drug if it had not done so voluntarily.
The FDA said neither Merck nor the agency had calculated the number of cardiovascular events in the general population.
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Some answers about the Vioxx recall
Q. If I've been on Vioxx, do I face a higher risk of heart problems in the future?
A. "The answer to that is almost certainly `no.' The drug's effects disappear very quickly," so stopping it should reverse risk, said Dr. Alastair J.J. Wood, associate dean of Vanderbilt University Medical Center.
Q. Is it safe to stop taking Vioxx suddenly, or should people go off the drug slowly?
A. People can and should stop taking the drug immediately. It is used to treat only arthritis pain symptoms, not the underlying disease.
Q. What made Vioxx so good for arthritis?
A. Many pain relievers called non-steroidal anti-inflammatory drugs work against two enzymes, cox-1 and cox-2, that cause inflammation and pain. Cox-1 is found in the stomach, and drugs that attack it often cause upset stomachs and ulcers. Vioxx and other so-called cox-2 inhibitors attack just that enzyme, minimizing stomach side effects.
Q. Are other cox-2 inhibitors safe?
A. All drugs of this type can raise blood pressure, but only Vioxx has been linked to higher risk of heart attack, stroke and other cardiovascular problems, FDA officials say.
Q. Can I get a refund on unused Vioxx?
A. Yes. Merck will require patients to mail back the unused drug in the original container, along with a pharmacy receipt, to: NNC Group, Merck Returns, 2670 Executive Drive, Indianapolis 46241. A note with the patient's name, address and phone number should be included.
More instructions and information are available through the Internet at www.vioxx.com and www.merck.com or by calling (888) 368-4699.