The elevated cardiovascular risk associated with Merck & Co’s COX-2 inhibitor Vioxx is not maintained after the drug is halted, according to new data.

Merck said yesterday that a preliminary analysis of the off-drug follow-up period in its APPROVe study of Vioxx found no statistically significant difference in the risk of heart attacks or stroke in patients who had previously taken Vioxx compared to those who had previously taken placebo.

The results could be an asset to Merck in its legal battles with former Vioxx users who claim the drug was responsible for cardiovascular thrombotic events they suffered, as it will undermine claims by those who had an event after they stopped taking the drug. More than 11,500 lawsuits have been filed against Merck by people, or their survivors, claiming to have been harmed by Vioxx.

Merck has vowed to fight each case one by one. The new data come after a bad spell in the courts for the drugmaker, with the last two cases resulting in multimillion damages against the firm.

Last month, a Texas court awarded $32 million in damages to the family of a man who died of a heart attack whilst on Vioxx for less than a month. Earlier in April, a New Jersey court awarded $13.5 million to a man who had a heart attack after taking Vioxx for four years, but dismissed another claim involving a plaintiff who could not prove long-term use of the drug. Merck is appealing both these verdicts.

The APPROVe results, originally designed to see if the drug was effective in preventing colorectal cancer, were initially reported in September 2004, and found an increased relative risk for heart attack and stroke beginning after 18 months of Vioxx treatment. The data was instrumental in Merck’s decision to take Vioxx off the market in the same month.

The new APPROVe data found that there were 28 thrombotic events in the Vioxx group, compared to 16 among those on placebo, but this difference was not statistically significant.

Meanwhile, Merck said a Vioxx lawsuit that was scheduled to begin on July 31 in Tampa, Florida, has been postponed at the request of the company and the plaintiff. The next case is due to be heard in New Jersey on June 5.