U.S. FDA staff mixed on AstraZeneca drug

WASHINGTON (Reuters) - U.S. reviewers gave mixed views on AstraZeneca Plc's (AZN.L) experimental blood thinner but the company's shares rose on investor optimism that an advisory panel will back the potential blockbuster drug.

The main issue facing Brilinta is a lack of benefit for North American patients in a large company study. That conflicted with a sharp reduction in deaths and heart attacks for patients overall.

AstraZeneca has suggested higher aspirin doses in the United States could account for the differences.

But in documents released on Monday, FDA reviewer Thomas Marciniak said "aspirin dosing does not explain the disparate results" between U.S. patients and other countries.

Other FDA staff, in memos prepared for an advisory panel that meets Wednesday, seemed willing to accept the differences.

Reviewers in the agency's office of pharmacology recommended Brilinta's approval with a post-market study "aimed to reconcile the findings" from the United States.

Another FDA reviewer, Dr. Robert Fiorentino, wrote that "it seems difficult to discount outcomes, particularly a benefit in all-cause mortality, observed in over 17,000 subjects" outside the United States.

AstraZeneca shares gained 3.9 percent on the New York Stock Exchange after the FDA documents were released.

"The FDA commentary points to a somewhat more positive outcome than expected," said Viren Mehta, principal at Mehta Partners in New York.

Mehta said some investors had been concerned that the FDA might object that Brilinta was compared with a standard dose of conventional blood clot preventer Plavix, rather than a twice higher dose that has become the "new normal" dose used by many doctors.

The FDA's Marciniak said AstraZeneca's main study of Brilinta was generally well-run but had incomplete follow-up rates that were "concerning."

AstraZeneca is counting on Brilinta to help offset the looming loss of patent protection on key 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.

(Reporting by Lisa Richwine; additional reporting by Ransdell Pierson in New York; Editing by Tim Dobbyn)