Merck & Co. Inc.‘s painkiller Arcoxia offers a “marginal” advantage in gastrointestinal safety but seems “worse than” other pain drugs in terms of deaths and serious cardiovascular problems, U.S. regulatory staff said in documents released on Friday.

Merck conducted studies on Arcoxia comparing it to a placebo, naproxen and other medicines known as nonsteroidal anti-inflammatory drugs.

“The results appear to demonstrate that (Arcoxia) is worse than each comparator” with regard to deaths and serious cardiovascular problems, Food and Drug Administration staff reviewers wrote in an analysis posted on the agency Web site.

The FDA told Merck last October Arcoxia was “approvable” after additional safety and effectiveness data were reviewed. The agency will seek input later this month from an outside advisory panel on the risks and benefits of Arcoxia and other painkillers.

Merck believes Arcoxia “has the potential to become a valuable therapeutic alternative,” company spokesman Chris Loder said. The firm believes it would be inappropriate to further discuss the drug before the panel meeting, Loder said.

Arcoxia is Merck’s successor to Vioxx, the arthritis drug the company pulled from the market last year after it was linked to heart attacks and strokes. Both drugs are part of a class called COX-2 inhibitors.

“It looks like this spells trouble for Arcoxia, although we already knew the drug was going to have a tough time getting approved because of concerns it raises blood pressure and causes fluid retention,” said Robert Hazlett, an analyst for Suntrust Robinson Humphrey.

Even if approved, some analysts have previously said they doubt Arcoxia could garner annual sales of more than $300 million, in part because of already swirling safety concerns. The drug is already sold in 51 countries in Europe, Latin America and Asia.

COX-2 inhibitors were developed to be gentler on the stomach and intestines than older painkillers, which can cause fatal bleeding.

In Merck’s studies of Arcoxia, the drug appeared to offer a “marginal” gastrointestinal advantage that was seen mainly when it was compared to naproxen in patients with osteoarthritis, the FDA reviewers said.

In a separate analysis, FDA reviewers said an experimental COX-2 inhibitor called Prexige, made by Novartis, showed it was safer on the gastrointestinal tract than other pain drugs. But the risks of heart attacks, strokes and deaths was “similar” to what was seen with Vioxx, the FDA reviewers said.

The FDA will ask the advisory panel if any COX-2 drugs should be marketed, according to a memo also posted on the FDA Web site. The agency wants to know “if there is a patient population for whom the risk is warranted, given the known potential for benefit,” the memo said.