Vitamin K antagonists after all, or possibly not?

Atrial fibrillation (AF) is a major public health problem, with an estimated prevalence of 2.5% in the Portuguese population aged 40 and over according to the results of the FAMA study published in 2010. 1 Only 37.8% of patients in the study were taking vitamin K antagonists (VKAs).One of the main limitations of chronic VKA therapy for the prevention of thromboembolism is the narrow therapeutic window for these drugs, international normalized ratio (INR) values often oscillating between reduced protection when below therapeutic levels and increased bleeding risk when above.The difficulty in maintaining patients within the therapeutic range (as reflected by percentage time in therapeutic range [TTR]) stems from the numerous interactions and complexity of warfarin metabolism.A TTR of >70% is considered ideal but this value is rarely achieved, even in patients with good control.In the large-scale clinical trials of the new oral anticoagulants (NOACs), TTR in the warfarin arm was 66% in RELY 2 (vs.dabigatran), 55% in ROCKET-AF 3 (vs.rivaroxaban), 62.2% in ARISTOTLE 4 (vs.apixaban) and 64.9% in ENGAGE 5 (vs.edoxaban).A study of AF patients in the UK General Practice Research Database included 27 458 warfarin-treated patients and 10 449 patients not treated with antithrombotic therapy.The mean TTR of treated patients was 63%.However, risk reduction is clearly proportional to the effectiveness of