New/direct oral anticoagulants (NOAC/DOAC), like apixaban and rivaroxaban, are an interesting alternative to unfractionated or low molecular weight heparin relayed by oral anti-vitamin K anticoagulants (VKA) for the treatment of venous thromboembolism and atrial fibrillation. This new generation of anticoagulants directly inhibit a factor in the blood coagulation pathway and have a wide therapeutic range overcoming several practical issues associated with VKA therapy including the need of routine coagulation monitoring potentially simplifying patient management. However, despite this wide therapeutic range, a large interindividual dose variability related to factors such as age, body surface, smoking, concomitant diseases as well as differences in drug metabolism, could put susceptible patients at risk for uncontrolled bleeding. Both rivaroxaban and apixaban are cleared primarily via cytochrome P450 (CYP) mediated hepatic metabolism, mainly CYP3A, and renal excretion, involving the P-glycoprotein (P-gp). Both CYP3A and P-gp activity show important interindividual variations due to drug interactions and/or genetic polymorphisms in corresponding genes.