A state-of-the-art antiblood-clotting drug developed by Bristol-Myers Squibb (NYSE:BMY) and Pfizer (NYSE:PFE) has won a second, crucial approval for sale in the European Union, the companies announced Tuesday in a joint press release.

The European Commission gave the nod to Eliquis, the companies' brand name for apixaban, for use by patients suffering from atrial fibrillation. This condition is the irregular, rapid contraction of fibers in the heart muscle, and is one of the leading causes of improper clotting and thus stroke.

Eliquis, which thins the blood as a means of fighting such clotting, had previously been approved for sale in the EU only for the prevention of deep-vein clotting in patients recovering from hip or knee replacement surgery. The new approval significantly widens the market for the drug. According to the two companies, around 6 million Europeans are afflicted with atrial fibrillation.

Eliquis belongs to a new generation of anticlotting drugs aiming to supplant the existing standard, warfarin. Although the latter is effective and inexpensive, it requires constant blood testing in order to monitor proper dosage.

Eliquis has not yet been approved by the U.S. Food and Drug Administration. After two delays, the regulator has said it will hand down a decision by March 17.

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