MERCK, the American drug company, is facing potential legal claims of $18 billion (£10 billion) after a court in Texas awarded $253.4 million in damages to a widow whose husband died after taking Vioxx, the painkiller.

Shares in the company dropped more than 4 per cent after the jury reached the verdict over the death of Bob Ernst, who died in 2001 of heart arrhythmia, or irregular heart beat, after taking Vioxx for eight months. Merck plans to appeal against the judgment.

Merck took the popular pain reliever off the market last September, after a study found that it doubled patients’ risks of heart attacks and strokes after 18 months of use.

Last night’s surprise decision by a state court in Angleton, Texas, is especially damaging because the drug company initially had been expected to win against what was considered to be a weak case.

Jason Napodano, an analyst with Zacks Investment Research, said that many people on Vioxx with cardiovascular problems would be likely to file a lawsuit. More than 4,000 cases have been filed so far. Merck has set aside $675 million to fight the lawsuits.

Mr Napondano said: “A Merck loss means that the number of cases against them increases tenfold.”

Mark Lanier, the plaintiff’s lawyer, told the jury that Bob Ernst, the plaintiff’s late husband, had died of a heart attack. Maria Araneta, who performed Ernst’s post-mortem examination in 2001, testified that although her report had said that Ernst had died of an arrhythmia, it was likely that he had suffered a heart attack. Dr Araneta said that Ernst probably had suffered a heart attack because a clot blocked the bloodflow in an artery that was already clogged with plaque.

Benjamin Zipursky, a professor at Fordham University School of Law in New York, said: “A Merck loss means the jury believes the plaintiff’s story about the company’s wrongful conduct. That carries into the future.”

The damages award combines Ernst’s lost pay as a produce manager for Wal-Mart, mental anguish, loss of companionship and punitive damages. He was 59 when he died.

Next month, Merck faces a trial in Atlantic City, New Jersey, brought by Michael Humeston, a former postal worker who had a heart attack in 2001.

In November, the first of 1,800 federal cases will be heard in New Orleans. The case concerns Richard Irvin, a Florida man who was taking Vioxx for a month before his death in 2001 from a blood clot in his heart.

Scientists have speculated that Vioxx causes cardiovascular problems because it blocks a substance that keeps blood from clotting.

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club