UPDATE 1-Cardiologist questions safety of Lilly's prasugrel

(Adds cardiologist quotes, details on trials, byline)

NEW ORLEANS, Nov 10 (Reuters) - Researchers have overestimated the ability to administer Eli Lilly and Co's LLY.N experimental prasugrel blood thinner without causing dangerous bleeding, a prominent cardiologist said on Monday.

U.S. regulators in recent months have twice delayed a decision on whether to approve prasugrel, a blood clot preventer being developed in partnership with Daiichi Sankyo 4568.T that would compete with Bristol-Myers Squibb Co's BMY.N Plavix.

Prasugrel proved far better able than Plavix to prevent dangerous blood clots in a large trial called Triton whose results were unveiled last year

But it was associated with a far higher degree of serious bleeding than Plavix, raising concern whether the U.S. Food and Drug Administration would deem its potential benefits worth the risks.

The Triton study involved patients who underwent angioplasties to clear clogged coronary arteries.

Researchers of the Lilly-sponsored trial had theorized that prasugrel could be safely given, as long as it was not taken by three groups shown to have the highest bleeding risk in the trial: patients weighing less than 130 pounds, those aged 75 or older, or those who had previous strokes or so-called mini-strokes.

But Dr. Sanjay Kaul, a cardiologist with Cedars-Sinai Heart Institute in Los Angeles, said on Monday that theory was at odds with scientific facts.

“The investigator analysis is off target because they could not draw the conclusion, based on the data, that bleeding risk is higher in these (supposed) hi-risk patients,” said Kaul, who is making several presentations on prasugrel at the annual scientific meeting here of the American Heart Association.

Kaul specializes in analyzing results of published trials.

Kaul said the risk of serious bleeding in the supposedly high-risk patients was 42 percent higher than with Plavix, compared with 24 percent higher risk among other patients receiving prasugrel.

Although the bleeding risk for the “high-risk” groups was numerically higher than for the “non-high risk” patients taking prasugrel, it was not statistically significant, he said in an interview.

“So you cannot identify which patients should be excluded,” he said, adding that too few patients were tested in Triton to draw any firm conclusions about which groups were at greater or lesser bleeding risk.

In Triton, prasugrel was 19 percent more effective than Plavix in preventing cardiovascular death, nonfatal heart attacks and strokes. But it was 32 percent more likely to cause serious bleeding.

Kaul said the negative bleeding findings should not have been a great surprise because worrisome bleeding risks were seen in an earlier and smaller pilot study of prasugrel.

“That should have caused a red flag,” said Kaul, who speculated the FDA could delay prasugrel’s approval for several years until Lilly completes another large prasugrel study that is underway.

But he said the agency would likely approve the drug relatively soon if Lilly can provide the agency data showing prasugrel is still effective but safer at a lower dose than the one used in the Triton study.

“This is a good drug but we need to be able to identify the maximum benefits of the drug and to come up with innovative ways to minimize the risk of bleeding,” said Kaul.

Even if approved, however, Kaul predicted prasugrel is likely to be a “niche” product.

“I don’t think it will be widely used, based on the bleeding concerns,” Kaul said, predicting that aspirin and Plavix will remain treatments of choice. (Reporting by Ransdell Pierson; Editing by Tim Dobbyn and Carol Bishopric)