A federal judge overturned a jury’s recent $50 million award against Merck & Co. (MRK) in a lawsuit filed by a Vioxx user.

The $50 million damage award in the federal Vioxx case was excessive, and a new trial must be held on damages for a retired FBI agent who suffered a heart attack after taking the painkiller, a federal judge ruled Monday.

“No reasonable jury could have found” that Gerald Barnett was entitled to $50 million in compensatory damages, U.S. District Judge Eldon E. Fallon ruled.

In the New Orleans verdict earlier this month, the federal jury, comprised of eight men, deliberated for about four hours before awarding $50 million in compensatory damages to Mr. Barnett, 62 years old, who had taken the painkiller for 33 months. The jury awarded Mr. Barnett an additional $1 million after attorneys for both sides presented brief arguments in a punitive damages trial.

In finding for Mr. Barnett, the jury voted Merck was negligent in failing to adequately warn Mr. Barnett’s treating physician of Vioxx’s risks and that the drug was a cause of the plaintiff’s heart attack. The jury also found Merck had knowingly failed to disclose information about the drug’s risks.

Merck had argued Mr. Barnett had a number of risk factors for a heart attack, including gender, age, family history of heart disease, high cholesterol and documented cardiovascular disease. Phil Beck, Merck’s lead trial lawyer in the case, told jurors that Mr. Barnett suffered a “mild” heart attack and continued to lead an active life.

Merck withdrew Vioxx from the market in September 2004 after a study known as Approve linked the drug to an increased risk of heart attacks and strokes in patients taking the drug for 18 months or longer. The New England Journal of Medicine, which published the Approve study in February 2005, recently issued a correction over the 18-month threshold, contradicting the company’s position that the drug doesn’t increase risk of heart attacks and strokes to people who took it for less than 18 months.

Each verdict is critical for the Whitehouse Station, N.J.-based drug maker because in mass-tort litigation the early cases are typically used to set the parameters for eventual settlement negotiations.

Both sides have been wrangling over which of the 16,000 cases facing Merck to try first. Christopher Seeger, a key figure in the coordination of plaintiffs attorneys’ efforts on Vioxx, had said before the verdict in New Orleans that the Barnett case was the first true plaintiffs’ pick.