Final answer:
Patients with a preexisting deficiency of vitamin K are at increased risk of warfarin-induced skin necrosis.
Step-by-step explanation:
The risk of warfarin-induced skin necrosis is increased in patients with a preexisting deficiency of vitamin K. Vitamin K plays a crucial role in the clotting process, and a deficiency can lead to impaired clotting function, increasing the risk of skin necrosis as a side effect of warfarin therapy.