Warfarin is an anticoagulant drug that works by inhibiting vitamin K dependent clotting reactions. While on the drug, it is important to either avoid foods with vitamin K or to maintain a consistent intake. Dietary vitamin K will alter the pharmacodynamics of the drug and change the resulting INR. Regular INR checks are initially critical to achieving therapeutic anticoagulation, however, once established, weekly INR checks are no longer required unless a change occurs. More common is once a month INR checks. Warfarin is metabolized by the liver via the cytochrome P450 CYP2D9 pathway and competes with many other drugs that utilize that same pathway. When initiating warfarin, the initial inhibition of the function of protein C and protein S will result in a transient hypercoagulability, resulting in skin necrosis. To avoid this, patients starting warfarin must be bridged for at least 5 days with another anticoagulant drug, such as enoxaparin.