A painkiller proposed as a successor to Vioxx may substantially increase the risk of stroke and heart attack and is no more effective for pain relief than other drugs of the same class, a federal drug safety expert said Thursday.

Safety studies done on the proposed drug, Arcoxia, are neither adequate nor reasonable to support its approval, Food and Drug Administration scientist Dr. David Graham told a panel of agency advisers. Graham has been a leading critic of Vioxx, also known as rofecoxib.

"What you're talking about is a potential public health disaster," Graham said of Arcoxia. "We could have a replay of what we had with rofecoxib."

Merck & Co. Inc. seeks FDA approval to sell Arcoxia, also known as etoricoxib, to treat the signs and symptoms of osteoarthritis. The Whitehouse Station, N.J., company withdrew Vioxx in 2004, after it was linked to a higher risk of stroke and heart attack when compared to dummy pills.

A Merck official said the company has "comprehensively characterized the safety and efficacy profile" of Arcoxia. The prescription drug is the first of its class to seek FDA approval since Merck withdrew Vioxx.

"We at Merck believe etoricoxib represents a valuable treatment option for patients with osteoarthritis. We would like to emphasize there is more long-term safety data ... for etoricoxib that any other NSAID," said Peter Kim, president of Merck's research laboratories.

An estimated 21 million Americans suffer from osteoarthritis. NSAIDs, or nonsteroidal anti-inflammatory drugs, are a common treatment. Arcoxia and Vioxx are types of NSAIDs called Cox-2 inhibitors, developed to be gentler on the stomach.

The FDA said this week that new NSAIDs that increase the risk of stroke and heart attack shouldn't be approved if safer alternatives are available.

The FDA convened a panel of expert advisers to weigh whether to recommend the agency approve Arcoxia. The FDA isn't required to follow the advice of its advisory committees but usually does. Merck hopes FDA will make a final decision by month's end.