Analysis of factors affecting time in therapeutic range control after warfarin administration

The protective efficacy of warfarin for cardiogenic cerebral embolism has been established. However, warfarin is generally administered to only approximately 35% of the atrial fibrillation patients who required warfarin therapy. It has been reported that international normalized ratio (INR) control was carried out appropriately in < 50% of such patients. Therefore, from the viewpoint of prevention of the onset and recurrence of embolism, the maintenance of a stable anticoagulant level is necessary. In warfarin therapy, in addition to INR control, time in therapeutic range (TTR) also markedly affects the efficacy of warfarin therapy. Therefore, we classified patients into two groups on the basis of the cutoff TTR ≥ 65% at which the inhibitory effect of warfarin on stroke has been observed. We aimed to examine the association between INR and TTR with the correction of the therapeutic efficacy of warfarin by analyzing the factors leading to poor TTR control. The most valuable finding of this study is that marked fluctuations of brain natriuretic peptide levels in patients with complication of heart failure was a risk factor for poor TTR control. Identification of the factors leading to the poor TTR control is useful for making the decision to switch to other anticoagulants, such as dabigatran or apixaban, or to continue warfarin by correcting risk factors in atrial fibrillation patients receiving long-term warfarin therapy.