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    • Friberg et al have indicated that

    2019-06-14

    Friberg et al. [17] have indicated that the CHA2DS2-VASc score is superior to the CHADS2 score in terms of stroke risk stratification, and the risk of stroke is extremely low among patients with a CHA2DS2-VASc score of 0 in whom antithrombotic therapy is not beneficial and may even increase the risk of ICH. They proposed that antithrombotic therapy should be performed in all patients with AF other than those with a CHA2DS2-VASc score of 0 and those with a high risk of bleeding (e.g., patients with a history of massive bleeding and patients with malignant hypertension). They expect that more patients will be indicated for antithrombotic therapy when novel OACs become more available as alternative agents to warfarin. In the absence of head-to-head comparative studies, it chenodeoxycholic acid is difficult to conclude that the 3 novel OACs (dabigatran, rivaroxaban, and apixaban) are equally useful. In an indirect model analysis, Banerjee et al. [18] concluded that the 3 novel OACs have net clinical benefits higher than warfarin in patients at high risk of bleeding and stroke. These drugs were shown to be superior (150mg bid dabigatran, apixaban) or noninferior (rivaroxaban) to warfarin in the prevention of stroke (for ischemic stroke prevention, a true efficacy parameter as AF causes ischemic and not hemorrhagic stroke, only dabigatran was shown to be superior), and have lower risk of ICH than warfarin. When the net benefit of new drugs is clarified in the future, it is expected that antithrombotic therapy will also be indicated for patients with a lower risk of stroke than those currently indicated for warfarin. However, dabigatran at 150mg bid was associated with an increased risk of extracranial bleeding in patients aged 75 years or older [19]. In patients <75 years of age, 110 and 150mg bid dabigatran were superior and comparable to warfarin, respectively, in terms of the risk of major bleeding. In the ROCKET AF trial, the risk of bleeding from gastrointestinal sites, including upper, lower, and rectal sites, was higher among patients receiving rivaroxaban than those receiving warfarin [13]. In a subanalysis of the ROCKET AF trial, rivaroxaban was comparable to warfarin in terms of the risk of bleeding in elderly patients [20]. Both apixaban and rivaroxaban required a dose reduction to 2.5mg bid and 15mg od, respectively, when they were given to patients with moderate renal dysfunction (creatinine clearance 30–50mL/min, and in case of apixaban, 2.5mg bid for a subset of patients with 2 or more of the following criteria: age >80 years, body weight <60kg, serum creatinine >1.5mg/dL). In the case of dabigatran, both doses were used in patients with mild to moderate renal dysfunction, and in a subgroup analysis of age and renal dysfunction it was shown that the 110mg bid dose may be considered in patients with a creatinine clearance of 30–50mL/min. Since patients with AF must continue antithrombotic therapy for the duration of their life, the safety of new antithrombotic agents in elderly patients is particularly important. Considering the racial/ethnic differences in bleeding, it may be preferable in Asia-Pacific countries that patients >75 years of age should receive warfarin as the first-line therapy, and patients >70 years of age should have INR 1.6–2.6, as recommended by the JCS 2008 guidelines. Alternatively, elderly patients (>80 years old) should receive dabigatran at the 110mg bid dose, whereas in those between 75 and 80 years of age the 110mg bid dose may be considered if they also have 1 or more risk factors for bleeding. Aging is known as the biggest risk factor of stroke and warfarin-associated bleeding. However, Singer et al. [21] have reported that the net clinical benefit of warfarin increased consistently with age, and was highest among patients >85 years of age. Friberg et al. [17] have reported that the net clinical benefit of warfarin is maintained even when the risk of ICH is assumed to double the risk of stroke. These findings support that warfarin is important to ensure effective prevention of stroke among elderly patients even when this drug increases the risk of bleeding in this patient population.