U.S. health regulators approved clot prevention drug Eliquis, developed by Bristol Myers-Squibb and Pfizer, for treatment in patients with atrial fibrillation, or irregular heartbeats.

The drug, also known as apixaban, was approved by European health regulators last month.

Eliquis belongs to a new class of medicines designed to replace decades-old warfarin for preventing blood clots in heart patients, or after a hip- or knee-replacement surgery.

Eliquis would compete against approved blood clot preventers such as Xarelto from Johnson & Johnson and Bayer, and Pradaxa from Boehringer Ingelheim.

Treating atrial fibrillation, which greatly raises the risk of strokes, is considered by far the largest and most important use for these new drugs.

The oral tablet Eliquis, like Xarelto, works by inhibiting a protein called Factor Xa that plays a critical role in blood clotting. Pradaxa has a slightly different mechanism of action.

However, Eliquis should not be taken by patients with prosthetic heart valves or those with atrial fibrillation caused by a heart valve problem, the U.S. Food and Drug Administration said in a statement.

About 5.8 million people in the United States suffer from atrial fibrillation, the most common form of heart arrhythmia, or irregular heartbeat.