A minor but material misstatement from Reuters: <A HREF="http://www.reuters.com/article/topNews/idUKL0923648620070709?rpc=44" target="_blank">http://www.reuters.com/article/topNews/idUKL0923648620070709?rpc=44</A> >> Rivaroxaban works by blocking a protein called Factor Xa, which plays an early role in the chemical process leading to blood clots. << Actually, FXa’s role is not really “early.” Rather, FXa is the pivot point in a feedback loop that greatly amplifies the production of thrombin.