NEW YORK (CNNMoney.com) - Merck, the no. 2 drugmaker in America, said on Tuesday that it made a correction to the study that led to the withdrawal of its arthritis painkiller Vioxx, but that it didn't change the results of the study.

Merck said it was correcting its "prior description of one of the statistical methods" used in the Approve study. But the drug maker also said this does not change the Approve results: that use of Vioxx increased the risk of blood clot-related heart attacks after 18 months of continuous treatment.

"We believe the correction does not change the results of the Approve study and does not change the conclusion of the Approve study," said Peter Kim, president of Merck Research Laboratories, in a teleconference.

The Approve study led to the removal of Vioxx from the market in 2004, precipitating Merck's (down $1.42 to $33.14, Research) 23 percent stock price plunge and wiping out $2.5 billion in annual sales. Since the drug was pulled, at least 11,500 lawsuits have been filed against Merck by former Vioxx patients and their families, blaming the drug for fatal and non-fatal heart attacks.

So far, five cases have gone to trial, resulting in two wins and two losses for Merck, with a split verdict in another.

This is the third instance in recent weeks that has drawn renewed attention to the Approve study.

On May 11, Merck announced the results of an "off-drug" follow-up study, that patients did not suffer an increased risk of heart attacks after they stopped taking Vioxx. While Kim of Merck said there was "no statistical difference" in heart attack risks in post-Vioxx patients, the company did acknowledge a slight increase in risk.

A few days later, The Wall Street Journal reported that an internal Merck document that summarizes the results of Approve showed that heart attack risk actually increases in the first four months after taking the drug. Merck dismissed the reported as "not scientifically appropriate."

These reports are likely to be used as fodder by lawyers from either side in the ongoing legal battle over Vioxx. The next case is on June 5, when plaintiff and former Vioxx patient Elaine Doherty faces off with Merck at New Jersey Superior Court in Atlantic City. Thousands of the cases have been filed against Whitehouse Station-based company in its home state of New Jersey.

To read about Merck's vaccine Gardasil, click here.