NEW YORK (CNN) - The chairman of pharmaceutical heavyweight Merck said Tuesday its arthritis drug Vioxx was pulled from the market at the earliest indication of problems.

What did pharmaceutical giant Merck know about the heart risks of Vioxx and when did they know it? Merck chairman, president and CEO, Raymond Gilmartin answers these questions. Play video (Real or Windows Media)

Raymond Gilmartin's comments came just two days before a scheduled hearing before the Senate Finance Committee on the safety problems with Vioxx. Gilmartin and top officials of the Food and Drug Administration are expected to testify.

"The first time we had a confirmed risk of Vioxx against placebo was the first time we got a call from the outside investigator on September 23rd, where the safety monitoring board had seen a higher risk of cardiovascular events that had developed beginning after 18 months and they recommended we end the clinical trial," Gilmartin told CNN's American Morning.

"After we looked at the data, within less than a week, we withdrew the drug voluntarily."

Vioxx was pulled from the market Sept. 30. In a statement, Merck (up $0.59 to $27.68, Research) said its decision was based on an ongoing colon cancer clinical trial that showed the drug raised the risk of cardiovascular complications in patients who have been taking the drug beginning after 18 months of the cancer treatment.

But leading cardiologist Dr. Eric Topol, in a commentary published in the New England Journal of Medicine Oct. 6, said Merck failed to act on earlier warning signs about its drug, resulting in possibly tens of thousands of people suffering heart attacks or strokes.

Topol also blamed the FDA for not mandating more trials.

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"Neither of the two major forces in this 5-and-a-half-year affair -- neither Merck nor the FDA -- fulfilled its responsibilities to the public," said the cardiologist with the Cleveland Clinic.

The drug was approved on the basis of a trial involving 8,076 patients that showed it caused fewer stomach ulcers than naproxen, another anti-arthritis drug.

But it took 1-1/2 years before details of the trial -- which showed an increase in strokes and heart attacks among patients who took the drug -- were published, Topol said.

And it was not until 2001 that the FDA Arthritis Advisory Committee discussed the drug's potential cardiovascular risks, he said.

Topol said he and his colleagues published an analysis of the data on Vioxx in August 2001 and concluded that a trial to assess cardiovascular impact of the drug was necessary.

He said such a trial should have been conducted in patients who already had coronary artery disease and arthritis requiring medication because complications would have been seen earliest in such patients.

Responding to Topol's commentary, Merck said in a statement that his article was "flawed in many respects," and that the company promptly disclosed adverse results to the FDA.

Gilmartin said Merck's randomized, clinical trial -- which began enrolling patients in February of 2000 -- was designed specifically to determine whether there was an increased risk of cardiovascular events in people taking the drug.

It took nearly a year, the chairman said, to enroll the 28,000 patients in the study.

"Remarkably, for the first 18 months there was no difference so it was consistent with all our other data and at 18 months the risk started to build and we saw the data, we withdrew the drug," said Gilmartin, who is also Merck's president and CEO.

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"I think it's important to keep in perspective here that the risk began only after 18 months of continuous use. .... The risk for any one individual for heart attack or stroke was very small, and heart attacks and strokes occur generally throughout the population for a variety of risk factors," he added. "Because someone is taking Vioxx doesn't mean Vioxx caused that event."

Merck launched Vioxx in the United States in 1999 and it has been marketed in more than 80 countries. The drug's worldwide sales last in 2003 were $2.5 billion.

Gilmartin refused to speculate how the company would handle the more than 400 lawsuits already filed against it related to the drug.

"The thing to keep in mind is that Merck is very financially strong. We have a very conservative balance sheet, we have strong cash flows, strong franchises in terms of ... other products that will continue to show strength in the marketplace," he said.