Why does warfarin take a couple of days to have its full effect?

Why does warfarin take a couple of days to have its full effect?

• A. The existing coagulation proteins must decrease
• B. It immediately depletes existing coag factors
• C. It inhibits platelet function
• D. It requires time for those proteins to decrease

Answer: (A)

Warfarin’s effect is delayed because it stops the production of new vitamin K–dependent coagulation factors, but the factors already circulating in the blood have to degrade before anticoagulation is evident. These factors (II, VII, IX, X, and proteins C/S) have different half-lives, so as each one turns over and is not replaced in its active form, the overall clotting potential gradually decreases. Only after enough of the existing factors have diminished does the anticoagulant effect become full, which is why it takes a couple of days to reach full effect. Warfarin does not directly inhibit platelets; its action is on the synthesis of coagulation factors.

Warfarin’s effect is delayed because it stops the production of new vitamin K–dependent coagulation factors, but the factors already circulating in the blood have to degrade before anticoagulation is evident. These factors (II, VII, IX, X, and proteins C/S) have different half-lives, so as each one turns over and is not replaced in its active form, the overall clotting potential gradually decreases. Only after enough of the existing factors have diminished does the anticoagulant effect become full, which is why it takes a couple of days to reach full effect. Warfarin does not directly inhibit platelets; its action is on the synthesis of coagulation factors.