Why is bridging therapy commonly used when starting warfarin?

• A. Immediate effect of warfarin
• B. No bridging needed
• C. Bridging with IV or SQ anticoagulants during the initial period
• D. Bridging with aspirin

Answer: (C)

When you start warfarin, its effect isn’t immediate. Warfarin blocks production of vitamin K–dependent clotting factors, but the body already has circulating factors, and the full anticoagulant effect takes several days to develop. In addition, levels of protein C and protein S drop quickly, which can create a temporary prothrombotic state at the start of therapy. To protect against early clotting during this vulnerable period, a fast-acting parenteral anticoagulant given by injection or IV is used and continued until the INR is in the therapeutic range. This bridging approach provides immediate protection while warfarin’s slower onset takes effect. Using aspirin as a bridge isn’t appropriate because aspirin is an antiplatelet agent and does not provide the needed anticoagulation coverage; it also adds bleeding risk without reliably preventing thromboembolism during the initial days of warfarin therapy.