Merck said it had adequately warned patients and doctors of Vioxx’s heart risks and that it never knowingly endangered patients.

The pace of Vioxx-related lawsuits, after soaring in 2005 and 2006, has fallen slightly this year, as plaintiffs’ lawyers shy away from cases where they lack strong evidence that their clients took Vioxx for several months before having a heart attack. Lawyers have withdrawn several cases as they were about to go to trial.

“It seems to have worked quite well,” Peter Schuck, a professor at Yale Law School who specializes in complex litigation, said of Merck’s strategy. “They have discouraged the plaintiffs’ bar from litigating these cases.” The legal system is not set up to try thousands of cases at once, and nearly all Vioxx lawsuits are caught up in the pretrial process.

Plaintiffs’ lawyers have tried to get the courts to combine all the potential suits into a single class action. But judges have rejected that tactic. Because the facts of individual cases can vary greatly, each case must be tried separately, courts have ruled.

So far, fewer than 20 Vioxx suits have reached juries, an average of 9 in each of the last two years. At this rate, the backlog of Vioxx cases will take years to work through and many plaintiffs may die before they get their day in court.

Even if they win, it will take years for plaintiffs to be compensated. Merck has appealed every case it has lost. In the case of Mrs. Ernst, if her award is upheld, she will not be paid before 2010 at the earliest, her lawyer, W. Mark Lanier of Houston, said.

Image Carol Ernst and her lawyer, W. Mark Lanier, on Aug. 19, 2005, after a jury in Texas awarded her $253.5 million. Credit... Pat Sullivan/Associated Press

After the 2005 verdict, analysts wondered how Merck would overcome evidence presented in the case, showing that the company had been concerned about Vioxx’s potential heart risks as early as 1997, two years before it began selling the drug.