Jurors in the first federal lawsuit against Merck & Co.'s painkiller Vioxx adjourned on Saturday and will return on Monday to try to reach a verdict despite telling the judge earlier in the day they were deadlocked.

The nine members of the panel resumed deliberations for about four hours after U.S. District Judge Eldon Fallon told them they should try to reach a unanimous verdict in the case concerning the 2001 death of a Florida man who took the drug for back pain.

In August, Merck (MRK) was found liable in state court for the death of a Texas man. A second trial in New Jersey state court exonerated the company in a separate case.

The jury began deliberations on Thursday afternoon in the case brought by the widow of 53-year-old Richard "Dicky" Irvin Jr., claiming her husband died of a heart attack in 2001 because he took Vioxx.

Irvin, a manager at a seafood distribution business, took Vioxx for less than a month before he suffered the fatal heart attack.

Merck faces more than 7,000 lawsuits claiming the Whitehouse Station, N.J., company hid for years the risks of heart attack and stroke linked to its blockbuster drug.

Analysts have said the company's legal costs to fight the cases could total several billion dollars.

Merck pulled Vioxx off the market in September 2004 after an internal study showed use of the drug for 18 months increased patients' risk of heart attack and stroke. Plaintiffs' lawyers have cited other studies that indicated the risks began far sooner.

On Thursday, the New England Journal of Medicine said Merck withheld information about the cardiac side effects of Vioxx when it presented the journal data from a key trial on the medicine's safety in 2000.

Read the NEJM's editorial (pdf)

Merck said it disclosed the events to U.S. regulators in 2000 and publicly in 2001, including in several press releases.

In the federal court case, Merck's lawyers argued Irvin had existing circulatory problems and died after plaque in his arteries broke loose and caused a blockage that triggered his heart attack.

The withdrawal of the drug, which was ultimately taken by more than 20 million people and generated more than $2.5 billion in sales for Merck in 2004, contributed to a $25 billion decline in the company's market capitalization.

The Texas widow who won the first case against the company in state court in August was awarded $253 million in compensatory and punitive damages, although that amount is likely to be trimmed to about $26 million because of Texas limitations on damage awards.