**Question:** Warfarin induced skin necrosis is more common in patients with

A. Hepatic dysfunction
B. Renal dysfunction
C. Older age
D. Lack of vitamin K

**Core Concept:**
Warfarin is an anticoagulant drug that inhibits the synthesis of clotting factors II, VII, IX, and X by blocking vitamin K-dependent clotting factor synthesis. Vitamin K is an essential cofactor in the synthesis of these factors, which are required for blood clotting. Warfarin-induced skin necrosis (WISN) is a rare but severe complication of long-term anticoagulation therapy with warfarin.

**Why the Correct Answer is Right:**
Warfarin-induced skin necrosis (WISN) is more common in patients with hepatic dysfunction (option A). Hepatic dysfunction can lead to decreased clearance of warfarin, resulting in increased drug levels and thus increased risk of WISN.

**Why Each Wrong Option is Incorrect:**
1. Renal dysfunction (option B) increases the risk of bleeding, but does not directly affect warfarin clearance. Therefore, renal dysfunction does not increase the risk of WISN.
2. Older age (option C) may be associated with increased risk of bleeding, but age itself does not directly affect warfarin clearance or the risk of WISN.
3. Lack of vitamin K (option D) is not the primary risk factor for WISN, as WISN occurs despite normal vitamin K levels. Instead, it highlights the importance of considering the effect of warfarin on clotting factor synthesis, rather than just vitamin K status.

**Clinical Pearl:**
It is essential to monitor and adjust warfarin therapy according to the patient's liver function, as hepatic dysfunction increases the risk of WISN. Regularly assessing liver function tests can help prevent this severe complication.

**Correct Answer:** D (Lack of vitamin K)