- Associated Press - Thursday, November 18, 2010

Pfizer Inc. says it is halting a key study of its experimental blood thinner, apixaban, because of dangerous bleeding among patients with a history of heart disease.

The drug, co-developed with Bristol-Myers Squibb Corp., has been touted as a potential blockbuster drug that could prevent heart attack and stroke without the bleeding side effects associated with older medications.

But Pfizer says it is halting a 10,000-patient study of the drug because of “a clinically important increase in bleeding among patients.”

The New York-based company is studying the drug for other uses to prevent blood clots and stroke in patients with irregular heartbeats.

Apixaban works by blocking a clotting protein called factor Xa. That is in contrast to drugs like Plavix, which work by preventing platelets from sticking together.