Experimental blood thinner apixaban is 50% better than aspirin at preventing strokes, study says

Researchers have prematurely terminated a clinical trial of an experimental blood thinner because the drug proved to be much better than aspirin at preventing strokes caused by atrial fibrillation, researchers said Tuesday. The drug, called apixaban, is one of three new drugs that are expected to compete against the widely used blood thinner warfarin in a market that is thought to be worth at least $10 billion per year.

Atrial fibrillation is an irregular beating of the heart that allows blood to pool in the upper chambers of the organ, where it can form clots. These clots can then migrate to the brain to cause strokes. The most widely used treatment for atrial fibrillation is warfarin, which impedes clot formation. But as many as half of the estimated 2.2 million Americans with the condition either can’t use warfarin or won’t because it requires extensive and constant monitoring to make sure the dosage is neither too low nor too high. The only treatment for those patients currently is aspirin. But warfarin reduces the risk of stroke by about 40% compared with aspirin, so the latter is not very effective.

In the new study called AVERROES, a team headed by Dr. Stuart J. Connolly of McMaster University in Hamilton, Ontario, enrolled 5,600 patients with atrial fibrillation who could not take warfarin. The patients were randomized to receive either apixaban or aspirin. In June, the study’s data monitoring committee recommended that the study be halted early because of its success, and researchers have been eagerly awaiting the findings. Connolly reported at the European Society of Cardiology Congress in Stockholm that apixaban reduced strokes and embolisms by 54% compared with aspirin. About 1.4% of patients receiving the drug had major bleeding events -- a fear with all blood thinners -- compared with 1.2% of those receiving aspirin, he said. The results were “truly impressive,” Connolly said. Results from a study of 18,000 patients comparing apixaban directly to warfarin are expected next year.

Apixaban is manufactured by Pfizer Inc. and some experts predict that the company will seek marketing approval from the Food and Drug Administration based on the AVERROES study alone. Two other new blood thinners will compete with it. Praxada, manufactured by the German pharmaceutical company Boehringer Ingelheim, has previously been shown to be more effective than warfarin and it will be reviewed by the FDA next month. Xarelto, manufactured by Bayer AG, is currently undergoing testing and results are expected to be announced in November.

“These medications are going to change practice in the United States,” Dr. Ralph Brindis of the Oakland Medical Center, president of the American College of Cardiology, said at a Stockholm news conference.

Thomas H. Maugh II / Los Angeles Times