From Rivaroxaban to Warfarin: How to Switch, Safely

Mr Smith is a 62-year-old man with long-standing atrial fibrillation and a history of stroke, who is currently being treated with the novel oral anticoagulant (NOA) rivaroxaban 20 mg daily. He has tolerated this regimen for more than 2 years and has had no bleeding complications. However, he recently lost his job and because of loss of insurance benefits can no longer afford his rivaroxaban. His new insurance company is mandating generic warfarin instead.

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Answer: B-Overlap warfarin with rivaroxaban to ensure that the patient is adequately anticoagulated during the switching period.

Discussion
Onset of action is characteristically slow with a vitamin K antagonist, such as warfarin. Because it can take 5 to 10 days to reach an INR in therapeutic range, both medications need to be administered concomitantly in order to adequately protect patients during the bridging period. Although the duration of the overlap period will vary based on the time it takes an individual patient to achieve a therapeutic INR, it is important to note that the INR measurement can be altered by the NOAs, especially the factor Xa inhibitors (rivaroxaban and apixaban). Therefore the European Heart Rhythm Association recommends that all INRs measured during the overlapping period be done immediately before the next dose of NOA is taken.¹

Therefore, if Mr Smith takes rivaroxaban at 9 AM every day, his INR should be measured immediately before this dose so that it reflects the effects of warfarin and is minimally confounded by rivaroxaban, which is at a trough. Furthermore, the guidelines recommend repeating the INR 24 hours after the last dose of rivaroxaban to ensure the anticoagulation is therapeutic. As soon as therapeutic INR is achieved, the rivaroxaban may be immediately stopped.

Finally, since it may take several half-lives for warfarin to be completely eliminated, close monitoring of INR in the first month is advised. At least 3 consecutive INR measurements should be obtained in that month in order to ensure that appropriate anticoagulation is achieved and the INR remains within the therapeutic range. 

 
Reference:
1. Heidbuchel H, Verhamme P, Alings M, et al. Euroepean Heart Rhythm Association pracitical guide in the use of new oral anticoaglants in patietns with non-valvular atrial fibrillation: executive summary. Eur Heart J. 2013;10.1093/eurheartj/eht134.