NEW YORK (Reuters) -
Two large drug makers, Eli Lilly and
Co and Daiichi Sankyo Co Ltd, face a critical U.S. decision
this week on their shared blood-clot preventer that could
dramatically boost their bottom lines.

“It's by far the biggest event at Lilly for quite some
time,” said David Heupel, a portfolio manager with Thrivent
Investment Management.

The decision by the U.S. Food and Drug Administration on
whether to approve the drug, prasugrel, could also sway the
stock prices of Bristol-Myers Squibb Co and Sanofi-Aventis,
which co-market a rival clot treatment, Plavix.

The deadline is September 26 for the FDA to rule on the
drug, which would be sold under the brand name Effient.

The main study for the drug contained mixed results —
potent effectiveness at preventing heart problems, but with
heightened bleeding risks — leaving Wall Street weighing
multiple scenarios for an FDA ruling.

Lilly stock could jump as much as 10 percent on an
approval, or fall as much as 10 percent if regulators require
additional extensive data, JP Morgan analyst Chris Schott said.

Lilly shares have fallen 14 percent so far this year,
compared with a 12 percent decline for the American Stock
Exchange Pharmaceutical Index of large U.S. and European
drugmakers.

For prasugrel, the FDA has declined to convene a public
meeting of its advisers, which it often does for new
experimental medicines to get further opinions. The lack of a
meeting has made the prasugrel decision difficult to handicap,
said Deutsche Bank analyst Barbara Ryan.

“This, along with a number of approval disappointments from
a seemingly more risk averse and less transparent FDA has made
investors wary of stepping into (Lilly) ahead of the” FDA
deadline, Ryan said in a recent research note.

Morningstar analyst Matthew Coffina gives prasugrel a 70
percent chance of approval at some point, and is expecting a
U.S. launch of the drug in mid-2009. Coffina sees it achieving
annual sales of $2 billion in about 10 years.

In a clinical trial, prasugrel was pitted against Plavix,
the current standard of care and one of the world's
biggest-selling medicines. Each treatment stops blood cells
called platelets from clumping together.

Results released last November showed that prasugrel was 19
percent more effective than Plavix in preventing cardiovascular
death, nonfatal heart attacks and strokes.

But prasugrel was 32 percent more likely to cause serious
bleeding, raising questions about its overall attractiveness to
doctors and patients and FDA examiners.

The bleeding risk in the study was most common among
patients weighing less than 135 pounds (61.2 kgs), over 75
years old or who had suffered a stroke previously. The FDA
initially was expected to rule on prasugrel in June, but
extended the review by three months to weigh more information.

The FDA could approve prasugrel, but with restrictions that
address these patients that are most at risk of bleeding,
analysts say.

Regulators could warn doctors against prescribing it for
those at-risk patient groups. Patients using the drug might
also be required to enroll in a registry to make sure they are
safely taking the medicine. Such a registry — deemed unlikely
by analysts — could dampen potential sales if physicians find
the conditions too burdensome.

JP Morgan's Schott said he would not be surprised if the
FDA required an additional short study testing a lower-dose
version in the bleeding-prone groups, which would likely delay
the drug's approval by a year.

Another scenario suggested the agency could require data
from an ongoing large 10,000 patient study that is testing
prasugrel against Plavix among patients with heart problems.
Results of that study are not expected until early 2011.

Such a prolonged delay could prevent prasugrel from making
deep inroads before cheap generic forms of Plavix reach the
market in late 2011.

“Generic Plavix will be a competitive threat no matter when
prasugrel is launched,” Morningstar's Coffina said. “If it were
delayed it would just make it that much harder.”

(Additional reporting by Ransdell Pierson, editing by
Leslie Gevirtz, Gary Hill)