By Kim Dixon

ORLANDO, Fla., Nov 4 (Reuters) - A key study finding that Eli Lilly and Co's <LLY.N> experimental anti-clotting drug boosts the risk of serious bleeding compared to the standard therapy prompted Wall Street analysts to question the outlook for the product on Sunday.

"I just wonder how many physicians are going to use the drug given the bleeding profile," Tim Anderson, an analyst with Sanford Bernstein, said on Lilly's conference call on Sunday.

Lilly sought to calm Wall Street following release of the 13,600-patient study at the American Heart Association's annual meeting in Orlando. The drug, prasugrel, showed impressive efficacy, according to doctors, but a 32 percent increase in serious bleeding is troubling to some.

Lilly and Japan's Daiichi Sankyo Co <4568.T> are seeking to take on Bristol-Myers Squibb's <BMY.N> Plavix. The study compared the two drugs in heart patients ranging from those with severe chest pain to heart attack.

Lilly cardiologist Anthony Ware noted the study's "net clinical benefit," which Lilly says proves the reduction seen in death from cardiovascular events outweighs deaths by bleeding.

"This sort of efficacy is hard to come by," Ware told analysts.

But analysts wondered about how that benefit was defined and if it would pass muster with U.S. regulators.

Lilly stood by its stance that it plan to file an application with the U.S. Food and Drug Administration by the end of the year.

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