TRENTON, N.J. (AP) – People who took the painkiller Vioxx were at increased risk of heart attack and stroke for at least a year after they stopped taking the drug, several doctors said Friday, challenging claims the drug’s maker had made the day before.

The doctors refuted the interpretation of a study by Merck & Co. Company officials had contended Thursday that users of Vioxx weren’t at increased risk of heart attack or stroke in the year after quitting the drug.

“Merck misrepresented the results of this study,” said Dr. Steven Nissen, a cardiologist at Cleveland Clinic who is leading a huge international study of the risks of several other painkillers.

Some doctors agreed, adding that former Vioxx users should be closely watched, although one said the risk appeared to decline somewhat during the one-year follow-up period.

Merck pulled Vioxx, once a $2.5 billion-a-year blockbuster, off the market in 2004 after a study found that over three years, Vioxx users had a 92 percent higher risk of heart attack, stroke and death than patients taking dummy pills.

The data released Thursday showed that in the follow-up year the risk could be up to three times higher for the Vioxx group, doctors said.

Merck contends the number of patients with complications was so small the data were not “statistically significant,” meaning something other than Vioxx could have affected their health.

But the doctors said that depending on how the data are calculated, patients who had taken Vioxx had a 64 percent to 85 percent higher risk of heart attack, stroke and death during the year after stopping the drug, compared to patients who were taking a placebo. The Vioxx group on average had a 74 percent higher risk of cardiac complications during the three years they took the drug and the one-year follow-up.

Data Merck supplied to The Associated Press Friday showed most patient deaths occurred during the study’s follow-up year, with 24 Vioxx users and 19 placebo users dying, compared with six in each group during the first three years of the study.

Asked about the doctors’ claim that Merck’s statements were misleading, Merck spokesman Michael Heinley said, “That would be their opinion.”

Heinley said the Whitehouse Station, N.J.-based company released all the data that it gave to the Food and Drug Administration and that it would not make Peter S. Kim, president of Merck Research Laboratories, available to the press.

During a teleconference with reporters and stock analysts late Thursday after Merck released the new data, Kim repeatedly stressed that there was no statistically significant increase in risk in the year after the study patients stopped taking Vioxx. During that year, there were 28 heart attacks or strokes in the Vioxx group, versus 16 in the placebo group.

Doctors said Merck was technically accurate that those numbers were too small to be certain Vioxx was the cause.

“That should clearly raise a concern, but it doesn’t prove … that risk,” said Dr. Scott Solomon, a cardiologist at Brigham & Women’s Hospital.

However, Dr. Bruce Psaty, an epidemiologist at University of Washington, said researchers instead would focus on other data clearly showing the risk of complications persisted.

Merck’s general counsel, Kenneth Frazier, said Thursday the new data showed that any Vioxx users who had a heart attack or stroke after stopping the drug wouldn’t have a legitimate lawsuit, but some doctors said the new data might help plaintiffs.

Merck faces about 11,500 Vioxx lawsuits and has lost half of the six cases that have been tried so far.

One analyst, Tim Anderson of Prudential Equity Group, wrote in a report Friday that the new data would have a “neutral” effect on Vioxx litigation.

Dr. Curt Furberg, professor of public health science at Wake Forest University School of Medicine, said one explanation for the persistent risk could be that Vioxx accelerates the buildup of plaque and hardening of the arteries, as some doctors believe. “If so, there is a risk all the rest of your life,” he said.

Merck shares fell 22 cents to $34.29 in trading Friday on the New York Stock Exchange.

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