Until 2010, the VKAs such as warfarin were the only available oral anticoagulants to protect against stroke in patients with AF. Although warfarin is efficacious in stroke prevention in the context of AF [17], its use is limited by certain practicalities. Slow onset, drug–drug and drug–food interactions [25], genetic polymorphisms in CYP2C9 [26] and the vitamin K epoxide reductase complex subunit [27] and patient factors including comorbidities all affect the pharmacokinetic properties, dosing requirements and anticoagulant effect of warfarin, making it an unpredictable drug requiring regular, sometimes intensive, monitoring of the international normalized ratio (INR) to achieve maximum therapeutic effect and minimum risk of harm to the patient. Even when tight control of anticoagulation is achieved, adverse haemorrhagic events can still occur in patients treated with VKAs.
The NOACs (previously referred to as new or novel oral anticoagulants [28]) were developed to provide efficacious anticoagulant drugs with rapid onset, a favourable side effect profile and predictable pharmacokinetic properties obviating the need for therapeutic drug monitoring [29, 30] (Table 2). Two classes of NOACs have been developed, and three drugs are currently licensed for use as anticoagulants in nonvalvular AF [31]: the direct thrombin inhibitors (dabigatran [21]) and the direct factor Xa inhibitors (rivaroxaban [22] and apixaban [24]). A further direct factor Xa inhibitor, edoxaban [23], has completed Phase III clinical trials and is licensed in Japan for use as thromboprophylaxis following lower limb orthopaedic surgery, for prevention of stroke and systemic embolism in nonvalvular AF and for the treatment and prevention of recurrent venous thromboembolism. Licence applications are in progress in Europe and North America for the use of edoxaban, particularly for stroke prevention and treatment of venous thromboembolism.