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Polymorphisms in two genes, CYP2C9 and VKORC1, account for about 40% of the variability in patients' warfarin responses. FDA-approved initial-dosing recommendations, based on these genetic parameters, increase time in the therapeutic range; however, because genotype-based dosing haven't been shown to improve clinical outcomes, these test are not reimbursed by Medicare. New oral anticoagulants, such as the recently licensed factor Xa inhibitor edoxaban (Savaysa), are as effective as warfarin, with more predictable pharmacodynamics and lower risk for bleeding.
In a previous trial, 21,105 adults with nonvalvular atrial fibrillation were randomized to receive warfarin (titrated to an international normalized ratio [INR] of 2.0–3.0) or daily edox…