Updated from 8:35 a.m.

Shares in the U.K-based drugmaker AstraZeneca ( AZN) fell Monday after an advisory committee of the Food and Drug Administration late Friday dealt a staggering blow to the company's experimental blood thinner Exanta, saying the risks of liver damage outweighed the benefits.

The panel rejected AstraZeneca's entire application that Exanta be approved for three uses related to preventing blood clots, Reuters reported Friday.

The FDA is expected to act on the panel's recommendations by late October. The agency doesn't have to follow its advisers' suggestions, but it usually does so.

Shares were off $1.60, or 3.7%, to $42.14.

AstraZeneca had asked the FDA to approve the drug for preventing blood clots in veins for patients undergoing knee-replacement surgery; preventing stroke and other clot-induced complications of the erratic heartbeat known as atrial fibrillation; and long-term prevention of blood clots in veins after a patient has gotten a standard blood clot treatment.

But once the advisory panel rejected the knee-replacement-surgery application, it was clear that Exanta was in trouble. Analysts had viewed knee surgery as Exanta's best chance because the European Union has approved the drug for preventing blood clots after elective knee and hip surgeries.

In the company's U.S. application, knee surgery would have only required, at most, 12 days of treatment with the drug, whereas the other indications would have required long-term use of Exanta.

In addition, the FDA panel rejected as inadequate the company's proposed monitoring plan to protect Exanta users against liver damage.

The advisory committee voted after markets had closed. AstraZeneca's stock closed Friday at $43.74, losing 66 cents, or 1.5%, on trading volume that was 6 times the daily average. But in after-hours trading, the stock was down another $1.29, or 3.3%.

On Thursday, an unfavorable FDA staff report used as guidance for the advisory committee sent the stock down 5.6% on trading volume that was 11 times greater than average. The report raised significant concerns about liver damage stemming from long-term use of Exanta.

AstraZeneca was hoping that the advisory committee would enable Exanta to become the first new oral anticoagulant in more than 60 years in the U.S . The "gold standard" is warfarin, a pill sold by several generic companies and also sold under the brand name Coumadin by Bristol-Myers Squibb ( BMY). Exanta is easier to administer than Coumadin, which requires periodic blood tests to measure its effectiveness. The AstraZeneca drug doesn't interact with as many drugs and foods as Coumadin does.

But the liver damage risks were too noticeable for the advisory panel. The FDA says that drug-induced liver injury is the top cause of acute liver failure, a rare disease that can produce critical illness in a few days, cause death, or necessitate a liver transplant. It's the leading reason why drugs are removed from the market and why the FDA requires restricted use of certain drugs and special monitoring of patients.

Depending on Exanta's performance, Merck ( MRK) could receive a royalty of as much as 20% of sales. That's the result of a 1994 joint venture between Merck and the then-independent Astra. The joint venture was restructured into a partnership in 1998, and the partnership was restructured after Astra merged with Britain's Zeneca in 1999. Right now, it appears Exanta won't be producing much revenue for either company.