Warfarin control in patients transitioning to warfarin after non-vitamin K oral anticoagulant (NOAC) therapy

Warfarin has long been the most widely prescribed oral anticoagulant. Introduction of non-vitamin K oral anticoagulants (NOACs) has provided anticoagulant options but also presented the potential challenge of transitioning between agents. Changes from NOACs to warfarin are particularly problematic with delays to therapeutic effect and limited real-world data regarding the impact on warfarin control. The aim of this study was to investigate the frequency of switching anticoagulants and the effect on warfarin control. Retrospective data was collected for patients at a warfarin program in Queensland Australia who had exited the program for NOACs plus those who had reverted to warfarin. Data included documented reasons for change and International Normalised Ratio (INR) results with time in therapeutic range (TTR) calculated as a measure of warfarin control. Over 5 years, a total of 3036 patients ceased warfarin to commence a NOAC but 142 (4.7%) reverted to warfarin. Majority of patients (60.6%) reverted to warfarin within 6 months of trialling NOACs with a median of 6 days to therapeutic INR. There was no significant difference in warfarin control before changing to NOACs and after reverting to warfarin (mean TTR 75%) but significantly more frequent testing and lower doses were required to achieve this control. Transitions from warfarin to NOACs results in almost a week to therapeutic effect and warfarin therapy may be further complicated by a need for increased frequency of testing. Further studies are required to refine transition strategies particularly from warfarin to NOAC and minimise potential risks to patients.