The first in a new class of blood thinners, a once-a-day drug called Xarelto, has been approved by the Food and Drug Administration for use in people with atrial fibrillation. Atrial fibrillation can cause blood clots that may lead to a stroke.

Xarelto was found to be as effective as warfarin, an older blood thinner known by its brand name Coumadin, based on a 14,000-patient study by Johnson & Johnson and Roche. Warfarin and other older blood thinners work by preventing blood platelets from sticking together, while Xarelto is the first of its type to work by blocking a clotting protein called factor Xa.

An alternative to warfarin has long been sought because the drug is notoriously hard to manage. Identifying the proper amount for a patient is difficult, and too much or too little can cause serious problems (internal bleeding, stroke).

"This approval gives doctors and patients another treatment option for a condition that must be managed carefully," said Dr. Norman Stockbridge, director of the FDA's cardiovascular and renal products division.

The FDA initially approved Xarelto in July to prevent strokes in patients undergoing hip and knee surgeries. With this latest approval, the drug is now approved for the more than 2 million Americans estimated to have atrial fibrillation.