Peripheral artery disease affects around 27 million people in Europe and North America, with sufferers at high risk of heart attacks, strokes and other complications.

The new study will compare AstraZeneca's medicine, currently only approved for patients with acute coronary syndromes (ACS), against older rival Plavix.

Sanofi's and Bristol-Myers's Plavix, which used to be the world's second-biggest selling drug, with annual sales of $9 billion, is now off patent and available as a cheap generic under the chemical name clopidogrel.

That poses a major challenge for AstraZeneca, which must differentiate its new product if it wants to win business from cost-conscious insurance companies and state healthcare providers.

Annual sales of Brilinta were forecast to reach $1.2 billion by 2016, according to a poll compiled by Thomson Reuters Pharma.

Brilinta has already proved itself against Plavix in a study of patients with ACS, or obstructed coronary arteries, and AstraZeneca hopes to extend that edge into another disease area.

The London-based drugmaker is facing loss of patent protection on many of its biggest-selling drugs, making Brilinta a particularly important new product.

The latest study is part of a wider program of clinical trials involving Brilinta and designed to show the benefits of the drug in reducing adverse cardiovascular events and death.

In total, the program is designed to include more than 51,000 patients worldwide.

(Reporting by Ben Hirschler; Editing by Dan Lalor)

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