A lot of money is riding on the data the drugmaker will disclose about its med this Sunday afternoon at the American Heart Association meeting in Orlando. At issue is whether its prasugrel blood thinner is believed to be safer and more effective than Plavix, a $7 billion franchise jointly marketed by Bristol-Myers Squibb and Sanofi-Aventis.

Until last week, Wall Street was optimistic prasugrel would be a winner and debut some time in late 2008. But then, Lilly did something curious - and ominous. The drugmaker suspended two small Phase II studies after data raised concerns about dosages used in some patient groups. Immediately, the move suggested problems with the larger Phase III trial to be released on Sunday, known as Triton, even though Lilly execs worked overtime to insist there was no linkage. And so here is what a couple of seasoned analysts are saying today about the big event.

“Our ‘best guess,’ consistent with our prior analyses, is that prasugrel will show higher efficacy than Plavix, but with the trade-off being higher rates of bleeding,” Sanford Bernstein pharma analyst Tim Anderson wrote investors this afternoon. “This probably leads to a drug that can be filed with FDA and other regulatory bodies for approval. However, far from certain is whether the drug can be approved. We continue to believe that higher bleeding rates were what caused the suspension of the phase II trials, and worry that the same may be seen in Triton.”

And here’s what Barbara Ryan of Deutsche Bank wrote today: “Our expectation continues to be that prasugrel may provide a superior efficacy outcome in the Triton trial, but is also more likely to have an increased bleeding liability that would temper its utilization (and we now speculate that individuals with some degree of renal impairment may be even more vulnerable in this regard at the 10 mg dose).”

This, of course, wouldn’t be good news for Lilly, which has been counting on prasugrel hitting the market next year and, shortly thereafter, be in a position to compensate for revenues that will be lost when such big sellers the Zyprexa antipsychotic lose patent protection.