A lawsuit against Merck & Co.'s (MRK) Vioxx (search) goes to trial in a Texas state court Monday in the first of thousands of cases claiming the pharmaceutical giant hid the risks of a popular painkiller.

The case in Angleton, near Houston, pits the family of deceased Texan Robert Ernst against the big drugmaker, which pulled Vioxx off the market in September after studies showed prolonged use could increase the risk of heart attack and stroke.

The lawsuit could help determine the direction litigation will take in the other state courts in New Jersey, California and Texas, and in the U.S. federal court in New Orleans, a legal expert said.

"The first case has a lot of impact on what comes afterward," said Chip Babcock, a partner at law firm Jackson Walker LLP in Houston.

Ernst had been taking Vioxx for six months when he died at age 59 in May 2001 of complications from heart arrhythmia (search). His family blames the drug for his death and is seeking unspecified damages from Merck, which is based in Whitehouse Station, N.J.

Judge Ben Hardin Monday is set to assemble a 100-member jury pool, which will be whittled down to 12 for a trial expected to last four to five weeks. Opening arguments in the case are likely to begin on Wednesday or Thursday.

Vioxx is the trade name for rofecoxib, which is part of the class of drugs called NSAIDs (search). It was touted as a pain and inflammation reliever that did not cause ulcers or gastrointestinal bleeding, a side effect of many such medications.

Merck, which faces nearly 4,000 lawsuits and 118 class-action suits, has said it tested Vioxx on nearly 10,000 patients during clinical trials and pulled the drug as soon as the danger of its prolonged use became clear.

The company argued in court documents that the heightened risk did not occur unless patients took the drug for longer than 18 months, far longer than Ernst had taken it.

Vioxx has also not been shown to raise the risk of heart arrhythmia, which was believed to cause Ernst's death.

"Both the nature of the death in this case and the facts concerning the (Ernst's) Vioxx use put the claims in this case totally outside the area of that controversy," Merck has said in court papers.

But the Ernst family's lawyer, Mark Lanier, said Merck had declined to disclose studies that showed risks began as early as six weeks after starting Vioxx usage, and that arrhythmia was one of those risks.

"Merck just won't show the public the studies," he said. " ... They ought to just come out and be honest."

A member of Merck's legal team, Jonathan Skidmore, denied the company had hidden any information about Vioxx.

"Merck disclosed information about the safety problems of Vioxx in a prompt and responsible manner," said Skidmore, a partner at Fulbright & Jaworski in Dallas. "There are no secret studies."

Last week, the Canadian government said it saw no reason not to reapprove the sale of Vioxx there, if Merck would submit a new application.

Merck has said it has not decided whether to seek that approval.