All are true about warfarin, except
**Core Concept**
Warfarin is a vitamin K antagonist that inhibits the production of vitamin K-dependent clotting factors in the liver, specifically factors II, VII, IX, and X, as well as proteins C and S. This leads to a decrease in the coagulation cascade, resulting in anticoagulation.
**Why the Correct Answer is Right**
Warfarin works by inhibiting the enzyme vitamin K epoxide reductase (VKOR), which is necessary for the recycling of vitamin K in the liver. This results in a decrease in the production of vitamin K-dependent clotting factors, leading to anticoagulation. Warfarin's effect is dose-dependent, and its anticoagulant effect is monitored by measuring the international normalized ratio (INR).
**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true about warfarin. Warfarin does indeed inhibit the production of vitamin K-dependent clotting factors, leading to anticoagulation.
**Option B:** This statement is also true about warfarin. Warfarin's anticoagulant effect is indeed monitored by measuring the INR, which takes into account the variability in reagent quality and instrument calibration.
**Option C:** This statement is true about warfarin. Warfarin can indeed interact with many medications, including antibiotics, antifungals, and anticonvulsants, which can affect its anticoagulant effect.
**Clinical Pearl / High-Yield Fact**
Warfarin has a narrow therapeutic index and requires careful monitoring to prevent both thrombosis and bleeding. It is essential to regularly check the INR and adjust the dose accordingly to maintain a therapeutic range.
**Correct Answer:** None of the above statements are false about warfarin.