Regulators in the USA have assigned a priority review to Pfizer and Bristol-Myers Squibb's much-touted bloodthinner Eliquis, a move which has surprised some observers.

The US Food and Drug Administration has accepted for review the firms' submission of Eliquis (apixaban) for the prevention of stroke and systemic embolism in patients with atrial fibrillation. With a priority review designation, the Prescription Drug User Fee Act goal date is March 28, 2012.

The submission is based on two Phase III trials of the oral Factor Xa inhibitor, which included 24,000 patients. They represent "the largest completed clinical development programme for stroke prevention in AF among novel oral anticoagulants", noted B-MS.

The priority review has led to raised eyebrows in certain quarters, seeing as how two new drugs in the AF area - Boehringer Ingelheim's Pradaxa (dabigatran) and Bayer/Johnson & Johnson's oral Factor Xa inhibitor Xarelto (rivaroxaban). Speedier reviews tend to be granted to drugs that offer major advances or provide a treatment where no adequate therapy exists.

Analysts see this as a major boost for Pfizer and B-MS. Deutsche Bank's Barbara Ryan issued a research note saying that the drug will likely get on the market six months earlier than many had expected. She added that "based upon the FDA’s designation and the Eliquis data, we believe that the drug will get a superiority claim to warfarin, and the survival data will at a minimum be included in the label".

Ms Ryan added that global Eliquis sales could reach $250 million next year, and hit a peak of $2.5 billion. In May 2011, the drug was approved in the European Union for the prevention of venous thromboembolic events in adults who have undergone elective hip or knee replacement surgery.