Topline results from the head-to-head study of the two drugs -- one of the largest comparative trials ever undertaken before approval -- underpin hopes for a pipeline product that analysts see as a potential multibillion-dollar-a-year seller.
The new medicine is a chance for AstraZeneca to prove its ability to get major new drugs to market at a time when older ones face patent expiry, following a drought of new product launches in recent years.
If approved, it will compete for business against one of the world's most successful medicines, since Plavix rakes in annual sales of some $8 billion.
AstraZeneca said on Monday the trial showed Brilinta worked better than Plavix in protecting high-risk patients from heart attacks and strokes, and it remained on schedule to submit the drug for regulatory approval in the fourth quarter.
Its shares jumped 6.3 percent by 7:15 a.m. EDT in a flat market for European drug stocks <.SXDP>.
Panmure Gordon analyst Savvas Neophytou said the clinical success should provide enough differentiation to make Brilinta a commercial hit. He currently predicts sales of $1.66 billion by 2014 but said this figure could rise once detailed results of the study are released.
Full results of the so-called Plato study -- a Phase III trial involving 18,624 patients with acute coronary syndrome given either Brilinta or Plavix -- will be presented at the European Society of Cardiology annual meeting in August.
Paul Mann of Morgan Stanley said Brilinta could represent a $3 billion sales opportunity -- potentially adding 15 percent to consensus earnings forecasts -- but there were still a number of uncertainties.
Ahead of presentation of side-effect data and details of the primary endpoint, the full commercial opportunity remains unclear, he said in a research note.
Questions about side effects and the fact Brilinta will take time to establish itself with doctors mean it may not be an immediate threat to Plavix, according to DZ Bank analyst Thomas Maul. Sanofi shares were off 1.2 percent.
The Plato study was designed to show at least a 13.5 percent relative risk reduction in the number of heart attacks, strokes and cardiovascular deaths for Brilinta versus Plavix, which is known generically as clopidogrel.
AstraZeneca did not specify the scale of its drug's superiority in a brief statement, simply stating that Brilinta had achieved a statistically significant primary efficacy endpoint.
The safety profile was in line with earlier Phase II studies, it added.
Challenging Plavix is a lucrative business but AstraZeneca does not have the market to itself. It also has to contend with Eli Lilly & Co
All three drugs work by stopping platelets -- tiny blood cells vital for the normal clotting process -- from clumping together and forming life-threatening clots in arteries.
AstraZeneca believes its drug has a key advantage because its action is reversible, lessening the risk to patients at risk of excess bleeding.
Brilinta is one of three pipeline drugs that investors are watching closely at AstraZeneca. The company has already filed a new diabetes drug, Onglyza, for regulatory approval and it will give a clinical update on cancer drug Zactima later this month.
(Editing by David Cowell)