Unit doses of factor Xa inhibitor compounds and methods of using these compounds for inhibiting blood coagulation in a human patient are taught herein. The unit dose of the factor Xa inhibitor compounds disclosed herein required to inhibit coagulation in a primate is lower than the unit dose required to obtain similar levels of coagulation inhibition in other animal models, such as rodents. Also taught are in vitro assays useful in predicting in vivo antithrombotic activity in humans.