When prescribing warfarin for home use after a thrombotic event, how long should the overlap with heparin therapy occur?

Warfarin is commonly prescribed for patients at risk of thrombotic events, such as deep vein thrombosis or pulmonary embolism, for long-term anticoagulation therapy. When starting warfarin therapy, it's important to ensure that anticoagulation is adequate, which is why it’s typically overlapped with heparin therapy.

The correct duration of overlap is generally around 5 days. This duration is recommended because it allows enough time for the INR (International Normalized Ratio) to reach a therapeutic level, ensuring that the patient is adequately anticoagulated. Warfarin takes several days to exert its full anticoagulant effect due to its mechanism of action—specifically, it inhibits vitamin K-dependent clotting factors that have already been produced.

During heparin overlap, the immediate anticoagulation provided by heparin helps prevent thrombosis until the warfarin reaches effective levels. After approximately 5 days or when the INR is within the therapeutic range, which is commonly between 2.0 and 3.0, the heparin can be discontinued safely.

The importance of this overlap period is to minimize the risk of thromboembolic events during the initiation of warfarin therapy, reducing the chance of complications associated