Merck & Co. Inc. researchers sought to reformulate the arthritis drug Vioxx five years ago to reduce its cardiovascular side effects, even as the company publicly played down data showing potential Heart attack risk, according to a report released early by The New England Journal of Medicine.

A study in March 2000 found that patients taking Vioxx were five times more likely to have Heart attacks than individuals using the generic medicine naproxen. Merck maintained at the time that this was a result of naproxen’s cardioprotective properties and not any defect in Vioxx.

The New England Journal of Medicine, citing an internal document, reported that company scientists were privately considering combining Vioxx with another agent to reduce the risk of Heart attacks and Strokes.

The document, a communication between Merck researchers and the company’s patent department, stated that the way Vioxx works to reduce pain might also increase cardiovascular problems. The researchers suggested a patent be sought for a combination drug mixing Vioxx with another agent to lessen the risk, according to the AP report.

A spokesman for Merck was not immediately available to comment. The AP report quoted a Merck official as saying the company believes it acted responsibly.

Merck pulled Vioxx off the market last fall after a study showed it doubled the risk of heart attack and stroke in patients taking the drug for more than 18 months.