Merck & Co. Inc. (MRK) Wednesday gave a glimpse of what some analysts say is likely to be its legal defense against allegations that it ignored early signs that its arthritis drug Vioxx (search) increased the risk of heart attack.

At a press conference in New York, the company's head of research and its legal counsel laid out the timeline for what Merck knew and when. The presentation comes as Merck braces for a wave of lawsuits from patients claiming they were damaged by the drug, which was pulled off the market last month.

"This sounds like the framework of a defense," said Kenneth Moll, managing partner of Kenneth Moll & Associates (search), a law firm that says it has filed the first class-action lawsuit on behalf of Vioxx patients. "But it's not much of a defense. They're saying they didn't know. Our answer to that is, 'You should have."'

Peter Kim, president of Merck Research Laboratories, said the first time that trial data definitively proved the problems with Vioxx was late last month. It showed that after long-term use, patients with colon polyps taking Vioxx had double the risk of heart attack and stroke as those taking placebo.

But the company initiated a trial known as VIGOR in January 1999 that tested Vioxx against naproxen, a painkiller. Patients taking Vioxx had four times the risk of heat attack as patients taking naproxen.

Merck has always claimed that naproxen protects the heart, so patients taking naproxen had fewer heart problems than those taking Vioxx. The company today conceded that this hypothesis was based on the fact that naproxen, like aspirin, inhibits the clumping together of blood platelets that can lead to heart attacks.

"There was plausibility that naproxen was cardio-protective," said Alise Reicin, vice president of clinical research at Merck Research Laboratories.

Merck said that once the results of the VIGOR trial emerged in March 2000, the company gave the information to U.S. regulators. Two years later, the company updated the prescribing information on the Vioxx label to reflect the results, a delay that some doctors have called into question.

Before the negative VIGOR data surfaced, Merck had begun trials to test whether Vioxx could be used to prevent or treat Alzheimer's disease (search). The results of 14 months of data were presented in June 2002. The company said it took an early look at the data in order to see if the same increased risk of heart attack seen in the VIGOR trial surfaced in the Alzheimer's trials.

Kim said that after 14 months there was no indication that Vioxx caused any greater risk of heart events.