The latest in a series of lawsuits brought by individuals claiming injury from Merck & Co’s withdrawn painkiller Vioxx got underway in New Jersey yesterday, and is expected to be a much harder case for the drugmaker to fight than those contested to date.

While earlier cases have involved patients who took Vioxx (rofecoxib) only for a brief period, the latest involves two individuals who were exposed to the drug over a protracted period.

Both plaintiffs, 59-year-old Thomas Cona and 77-year-old John McDarby, claim Vioxx was responsible for heart attacks they suffered, while their lawyers insist Merck was aware of the dangers with the drug and tried to hide the risks.

Merck is denying liability, saying that their underlying heart disease was more likely responsible for the heart attacks, and strongly refutes any allegations that it set aside patient safety for profit.

Merck pulled Vioxx off the market in September 2004 after a study showed the COX-2 inhibitor doubled the risk of heart attacks and strokes when taken for 18 months or more. Cona claims to have taken the drug for 22 months, while McDarby says he was on it for around four years.

Merck is till facing thousands of lawsuits brought by patients who claim Vioxx caused them harm, but so far has won three of the four cases that have come to trial, and lost another in which the plaintiff was awarded damages of $253 million (cut to $26 million under state capping laws).

And Merck is not alone in having to defend its COX-2 inhibitor in the courts. In June, the first court case involving another drug in the same class that is still on the market, Pfizer’s Celebrex (celecoxib), is scheduled to get underway.