U.S. advisers backed a potential blockbuster blood thinner from AstraZeneca on Wednesday, a victory for a company seeking new drugs to offset expiring patents on some of its best-selling medicines.

Members of a Food and Drug Administration panel voted 7-1 to recommend approval of Brilinta for patients suffering from heart attacks or chest pain who need drug therapy or an artery-clearing procedure.

Analysts predict Brilinta's sales will top $1 billion a year based on strong results showing the medicine reduced deaths and heart attacks.

AstraZeneca shares, which surged in the final hour of regular trading to finish 3.2 percent higher on the New York Stock Exchange, gained another 2.6 percent in after-hours trade to $52.84, following the panel vote.

The company overcame doubts about Brilinta's effectiveness in U.S. patients. In a clinical trial of 18,000 patients, the relatively small group from North America saw no benefit.

Panel members struggled to explain that result but voted 7-1 that the sharp reduction in deaths and heart attacks in other patients justified Brilinta's use in the United States.

The overall results are so striking, said panelist James Neaton, a statistician at the University of Minnesota.

Viren Mehta, an analyst with Mehta Partners in New York, said the lopsided vote in favor of Brilinta will prompt him to review his earlier conservative sales projections for the drug.

Brilinta has potential to be a big product, he said, especially as new uses of the drug are approved.

The FDA is supposed to make a final decision on Brilinta by September 16. The agency usually follows panel recommendations.

Anglo-Swedish drugmaker AstraZeneca is counting on Brilinta, known generically as ticagrelor, to help offset the looming loss of patent protection on drugs such as heartburn treatment Nexium and antipsychotic Seroquel.

Consensus 2014 sales forecasts for Brilinta stand at $1.1 billion, according to Thomson Reuters data. The company's total sales topped $32 billion in 2009.

The panel decision came out more positive than we certainly anticipated, Leerink Swann analyst Seamus Fernandez said.

AstraZeneca now could win approval for treating a broad range of patients with acute coronary syndromes, which includes heart attacks and chest pain, he said.

Fernandez said the final FDA ruling could slip beyond the September deadline, ... but I think we're going to see this drug on the market in the U.S. and Europe in 2011.

Brilinta would compete directly with Plavix, the standard anti-clotting drug now given to prevent heart attacks. Sold by Sanofi-Aventis and Bristol-Myers Squibb , Plavix is world's second-best selling drug with annual sales of about $9 billion.

In AstraZeneca's study, Brilinta proved better than Plavix in preventing heart-related problems linked to blood clots. After one year, 9.8 percent of Brilinta patients had suffered a heart attack, stroke or cardiovascular-related death, compared with 11.7 percent in the Plavix group.

Brilinta did not increase the chances of major bleeding, a serious risk of anti-clotting drugs.

But the AstraZeneca drug did not help the roughly 9 percent of patients who were from North America.

The company argued that higher aspirin doses routinely given in the United States might have interacted with Brilinta and a lower aspirin dose could have yielded benefits similar to those seen in other countries.

FDA reviewers questioned that theory, and panel members said they could not find an explanation.

There is great uncertainty about this issue, said Dr. Sanjay Kaul, the panel's chairman and a cardiologist at Cedars Sinai Medical Center in Lost Angeles.

Some panelists urged a post-approval study of the drug's effects in U.S. patients.

Plavix and Brilinta work by stopping blood platelets from sticking together and forming clots that can cause heart attacks and strokes.

AstraZeneca said it was pleased with the panel votes.

We look forward to working with the FDA as it continues to review the drug, AstraZeneca Chief Medical Officer Howard Hutchinson told reporters.

(Reporting by Lisa Richwine; Additional reporting by Ransdell Pierson and Bill Berkrot in New York; Editing by Robert MacMillan and Tim Dobbyn)