A clinical trial for Novartis AG’s experimental painkiller Prexige showed the risk of heart attack, stroke and death was “similar” to Merck & Co. Inc.‘s now withdrawn Vioxx, U.S. regulatory staff said in documents released on Friday.

Prexige, which is not yet approved in the United States, showed greater cardiovascular risks compared to naproxen but similar risks compared to ibuprofen, Food and Drug Administration staff said.

The trial also showed Prexige had an “advantage” over other pain drugs that can cause stomach problems.

“Definitely, Target showed a (gastrointestinal) advantage over” patients taking ibuprofen or naproxen, especially in those who were not taking aspirin, the FDA reviewers said in their analysis, which was posted on the agency’s Web site.

The documents were released ahead of an unusual three-day meeting later this month when an FDA panel of outside experts will discuss Prexige, Vioxx and other similar pain medicines.

Agency officials called for the meeting after a series of warnings since September over heart problems connected to both prescription and over-the-counter painkillers.

Novartis spokeswoman Kate O’Connor said it was important to note that the study did not produce definitive results but she had no comment on the Vioxx comparison. “I think it’s premature to comment on anything like that,” she said.

Some analysts said they were not surprised by the FDA staff’s comments since the agency earlier rejected the drug. “Almost all of this has been known,” said Deutsche Bank analyst Barbara Ryan.

Novartis shares closed down 7 cents at $47.84 on the New York Stock Exchange on Friday.

When the FDA rejected Prexige in 2003, it said it wanted to see complete results of a two-part trial called Target.

One part of the Target trial, which followed about 18,000 patients for 52 weeks, showed 40 cardiovascular-related problems, including 11 deaths, in patients who took Prexige, compared with 27 problems, including 8 deaths, in naproxen patients.

FDA staff said those findings “are consistent with findings for Vioxx,” the arthritis drug Merck pulled from the market in September after a study showed it raised the risk of heart attacks and strokes. Both drugs are part of a class called Cox-2 inhibitors.

A second arm of the trial found 19 cardiovascular reactions, including eight deaths, with Prexige compared to 21 reactions, including 10 deaths, with ibuprofen.

Naproxen and ibuprofen are part of a group of medicines called non-steroidal anti-inflammatory drugs, which can cause ulcers and other gastrointestinal problems.

“This study has not definitely answered the question whether lumiracoxib (Prexige) increases cardiovascular thrombotic risk compared to non-selective NSAIDs,” the staff wrote.

Novartis has said it may refile for U.S. approval in 2007. Prexige is approved in Britain and 20 other countries, but the company pulled its application for wider EU approval in November, saying it would provide more data.

In other FDA documents released Friday, FDA staff questioned Merck’s newer painkiller called Arcoxia, which they said showed “marginal” advantage over stomach problems but seemed to be worse than other pain drugs regarding deaths and serious cardiovascular problems.