Merck & Co’s Vioxx will face another jury this week – in Atlantic City, New Jersey – and will likely be feeling a weight on its shoulders as this is the first case to involve chronic users of the drug.

Vioxx was taken off the market after a study showed a doubling in the risk of heart attack in patients taking the drug for more than 18 months. The four trials that have come to a conclusion – of which Merck has won three – have all involved individuals who took Vioxx for the short-term relief of symptoms, and observers will be eagerly awaiting the verdict of this Atlantic City court case as a predictor of future decisions.

Merck has previously argued that plaintiffs could not have taken Vioxx sufficiently long enough to have developed heart problems; but it won’t be able to use this defence strategy in the upcoming trial.

Most recently, the judge ruled that Vioxx was not responsible for the death of Richard Irvin, a 53-year-old Florida man who died of a heart attack in 2001. But Merck is still facing an estimated 10,000 lawsuits, with previous estimates putting its liability at up to $50 billion.

And its position won’t be helped by resurfacing criticism of the VIGOR study – the trial that propelled Vioxx’ withdrawal from the market. The New England Journal of Medicine last year accused Merck of omitting data on three heart attacks – a charge the US drug giant vehemently denies – and renewed its criticism in another stinging editorial earlier this month.

But Merck is not alone in facing the jury, and this year will see the first trial to come against Pfizer, which still markets its COX-2 inhibitor Celebrex (celecoxib) but has, not surprisingly, seen sales slump dramatically as the Vioxx cloud hangs over the whole drug class.

The trial date is set for June 6 and will involve a 53-year-old from Alabama who blames Celebrex for a stroke she had in 2005 (see adjoining story).