Interpatient variability in the safety and efficacy of oral anticoagulation with 
warfarin presents several challenges to clinicians, thus underscoring the 
emergent need for new orally available anticoagulants with predictable 
pharmacokinetic and pharmacodynamic profiles and ability to target circulating 
clotting factors. Seven compounds including rivaroxaban, apixaban, betrixaban, 
and eribaxaban are orally available direct inhibitors of activated factor X 
currently in development for the prevention and treatment of venous 
thromboembolism and for thromboprophylaxis in patients with atrial fibrillation 
or following an acute coronary syndrome. At doses used in phase 2 and 3 clinical 
trials, rivaroxaban and apixaban demonstrated a predictable onset of effect, 
maximal plasma concentration, and half-life that was unaffected by age, renal, 
or hepatic disease. In clinical trials for the treatment and prevention of 
venous thromboembolism, rivaroxaban and apixaban produced equivalent or superior 
reductions in the development or progression of venous thromboembolism compared 
with either low molecular weight heparin or warfarin. Trials comparing the 
efficacy of rivaroxaban or apixaban to standard therapy for stroke prophylaxis 
in patients with atrial fibrillation are in process. Rivaroxaban, the sentinel 
compound in this class, is already approved in the European Union and Canada. It 
is likely to be approved for use in the United States in 2010.