American Board of Internal Medicine (ABIM) Certification Practice Exam

How long must anticoagulant administration overlap with warfarin?

1. 2 days

2. 3 days

3. 5 days

4. 7 days

The correct answer is: 5 days

The correct answer regarding the duration of overlap for anticoagulant administration with warfarin is five days. This is typically based on the pharmacokinetics of warfarin and the functioning of the coagulation pathway, particularly the half-lives of vitamin K-dependent clotting factors. When initiating warfarin therapy, it's crucial to ensure that the INR (International Normalized Ratio) reaches a therapeutic range, usually between 2.0 to 3.0, to provide sufficient anticoagulation and prevent thromboembolic events. Because warfarin has a delayed onset of action and does not affect existing coagulation factors right away, an overlapping anticoagulant, such as low molecular weight heparin (LMWH) or unfractionated heparin, is needed during the initiation period. The typical guideline is to continue the overlap until the INR is stabilized within the desired therapeutic range for at least 24 hours, which usually requires around five days of overlap to ensure that the anticoagulation effect of warfarin is adequate and that the risk of thrombosis is minimized. Additionally, it allows both the new treatment to adjust and the elimination of any pre-existing thrombotic risk that may have been present prior to starting war