How many days does Warfarin typically take to reach the therapeutic level mentioned in the material?

How many days does Warfarin typically take to reach the therapeutic level mentioned in the material?

• A. 1-2 days
• B. 3-4 days
• C. 4-7 days
• D. 8-10 days

Answer: (C)

Warfarin’s effect is delayed because it works by reducing the production of vitamin K–dependent clotting factors, not by quickly inactivating what’s already circulating. Those existing factors must be depleted before the anticoagulant effect shows up in the INR. Among the factors, the one with the longest time to fall to a therapeutic level is factor II, which drives the lag, so the full therapeutic effect typically emerges over several days. In practical terms, most patients reach the desired anticoagulation range after about four to seven days of steady dosing. That’s why a bridging agent like heparin is often used if immediate anticoagulation is necessary.

Warfarin’s effect is delayed because it works by reducing the production of vitamin K–dependent clotting factors, not by quickly inactivating what’s already circulating. Those existing factors must be depleted before the anticoagulant effect shows up in the INR. Among the factors, the one with the longest time to fall to a therapeutic level is factor II, which drives the lag, so the full therapeutic effect typically emerges over several days. In practical terms, most patients reach the desired anticoagulation range after about four to seven days of steady dosing. That’s why a bridging agent like heparin is often used if immediate anticoagulation is necessary.