But exactly why North American patients enrolled in the study did not benefit from Brilinta treatment remains a mystery.
That appears to be why the FDA yesterday refused to approve Brilinta, overruling last July's 7-1 vote for approval by an expert advisory panel.
The silver lining for AstraZeneca is that the FDA is not calling for a new clinical trial -- only for a new analysis of the study data.
During the panel meeting, the experts looked at several differences between North American and European study participants. The U.S. and Canadian patients took higher doses of aspirin, but the experts were left scratching their heads over how this might affect how Brilinta worked.
One hint is the U.S. and Canadian patients were less likely to take their medications exactly as prescribed. Brilinta wears off more quickly than Plavix -- which can be an advantage if further surgery is needed -- but that means missing just one of the drug's twice-daily doses could be dangerous.
Analysts predict that the FDA eventually will approve Brilinta, but that this won't happen before 2012.
Brilinta is approved in Europe, where it will be sold under the brand name Brilique.