The drug, made by privately-held Boehringer Ingelheim Pharmaceuticals, showed the effect in a new, yet-to-be published study, said David Graham, associate director for science and medicine at the FDA's Office of Drug Safety.
Mobic has become the top-selling prescription pain drug since Merck pulled Vioxx, and any possible heart attack risk is important as more patients take the drug, Graham said.
The statistical risk of heart attack was 1.37 for Mobic, compared to 1.32 with Vioxx and 1.09 with Celebrex.
Germany-based Boehringer argued against Graham's claims. "We've taken a look at our post-marketing data and see nothing to indicate excessive cardiovascular risk," the company spokesman said.
Mobic is classified as a Cox-2 in some countries but is not considered part of that group in the United States, where is its only classified as part of the larger NSAID class, a Boehringer spokesman said.
Aspirin, naproxen and other NSAIDs can cause ulcers and dangerous bleeding.
Abbott Laboratories (ABT.N: Quote, Profile, Research) , which co-markets Mobic in the United States, said last month it expected U.S. sales of the drug to hit $1 billion in 2005.
Shares of Abbott closed off 27 cents to $46.56 on the New York Stock Exchange.
JP Morgan analyst Mike Weinstein said this was the first time any heart risk for Mobic has been noted.
"The topic will likely now warrant some extra monitoring," he said in a research note.
The FDA approved Mobic in 2000 to treat osteoarthritis, and in 2004 for rheumatoid arthritis. (Additional reporting by Debra Sherman in Chicago)
