MKSAP Quiz: 5-day history of leg pain and swelling

MKSAP Answer and Critique

The correct answer is C: At least 5 days of LMWH plus warfarin with a target INR of 2 or higher for 24 hours. This item is available to MKSAP 16 subscribers as item 29 in the Hematology and Oncology section. More information is available online.

The best management of this patient's transition from parenteral LMWH to warfarin therapy requires at least 5 days of overlap with LMWH and warfarin therapy and an INR of 2 or more for 24 hours. Randomized clinical trials have demonstrated that 5 to 7 days of unfractionated heparin is as effective as 10 to 14 days when transitioning to warfarin therapy. Shorter durations of parenteral anticoagulation in the transition to vitamin K antagonists have not been tested and, theoretically, could confer a higher risk for recurrent thromboembolism. Warfarin acts as an anticoagulant by impairing hepatic synthesis of vitamin K-dependent coagulation factors rather than by directly inhibiting the function of already synthesized factors. Therefore, once an appropriate warfarin dose is initiated, the onset of therapeutic anticoagulation is dictated by the half-life of the coagulation factors. If a patient is receiving an adequate warfarin dose, it takes at least 5 days for vitamin K-dependent factor activity levels to decrease sufficiently for therapeutic anticoagulation (INR of 2-3) to occur. Consequently, parenteral anticoagulant therapy (LMWH) should be continued along with warfarin for at least 5 days and until a therapeutic INR of 2 or more for 24 hours is achieved to avoid an increased risk for recurrent thromboembolism.