An American jury has awarded $9 million (£5m) in punitive damages to a man who blamed his heart attack on Vioxx, the arthritis drug made by Merck.

The judgment, made in a New Jersey court, could strengthen the cases of other plaintiffs against the US pharmaceuticals giant, who have claimed that their health was damaged by the painkiller.

Vioxx was taken by around 20 million Americans before being withdrawn from the market in 2004. Merck now faces around 9,650 Vioxx court cases in America, and has said it will try them one at a time.

John McDarby, 77, the retired insurance agent at the centre of today's judgment, claimed that Merck failed to warn patients of the risks and misrepresented the potential dangers to physicians.

Carl Tobias, a law professor at the University of Richmond, told Reuters: "This is important because the punitive damage statutes in New Jersey set a very high bar for plaintiffs.

"The finding ... indicates that plaintiffs hurdled that very high bar. That’s a setback for Merck, they were contending of course that no punitive damages could be awarded."

The damages are in addition to $4.5 million already awarded to Mr McDarby, 77, who suffered a heart attack after four years on Vioxx.

In its only other loss in a Vioxx case, Merck was ordered last August to pay $253 million to the widow of a man who died after taking the drug for a short time. That amount will be reduced because the law in Texas, where the case was heard, limits punitive damages.

Shares in the drugmaker rose more than 1 per cent to $34.80 in early trading in New York following the news.

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Scott Henry, an analyst at Oppenheimer & Co, said: "I’m surprised investors are not greeting this with more pessimism. It is only one data point among many, but in no way is this a positive development.

"These awards will re-motivate the plaintiffs lawyers."

The trial, the sixth over Merck’s once-popular painkiller, was the first involving people alleging use of 18 months or more. The study that prompted Merck to voluntarily withdraw the drug found that risks doubled after 18 months’ use.

Today's decision followed a five-week trial that combined two cases: that of Mr McDarby, a retired insurance agent who took the drug for four years, and Thomas Cona, 60.

Mr Cona said he took the drug for 22 months before his 2003 heart attack but prescription records showed only enough for about seven months’ use. The jury rejected his claim that Vioxx was to blame.

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