**Core Concept**
Warfarin is a vitamin K antagonist that exerts its anticoagulant effect by inhibiting the synthesis of vitamin K-dependent clotting factors in the liver, including factors II, VII, IX, and X.

**Why the Correct Answer is Right**
Warfarin works by competitively inhibiting the reduction of vitamin K epoxide to vitamin K hydroquinone by the enzyme vitamin K epoxide reductase (VKOR). This leads to a decrease in the production of clotting factors, which are essential for the coagulation cascade. As a result, warfarin increases the prothrombin time (PT) and international normalized ratio (INR) in patients.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because warfarin does indeed have a narrow therapeutic index, requiring regular monitoring of INR levels to avoid either under- or over-anticoagulation.
**Option B:** Incorrect because warfarin is metabolized by the liver through cytochrome P450 enzymes, particularly CYP2C9, and its efficacy can be affected by genetic polymorphisms in this enzyme.
**Option C:** Incorrect because warfarin can interact with a wide range of medications, including aspirin, antacids, and antibiotics, leading to changes in its anticoagulant effect.

**Clinical Pearl / High-Yield Fact**
Warfarin has a long half-life and can take several days to reach its full anticoagulant effect, making it essential to monitor INR levels regularly, especially in the initial stages of therapy.

**Correct Answer:**