The anticlotting protein C and protein S are also inhibited, but to a lesser degree. Without sufficient active vitamin K 1, clotting factors II, VII, IX, and X have decreased clotting ability. Warfarin decreases blood clotting by blocking vitamin K epoxide reductase, an enzyme that reactivates vitamin K 1. The effects of warfarin may be reversed with phytomenadione (vitamin K 1), fresh frozen plasma, or prothrombin complex concentrate. Many other medications and dietary factors can interact with warfarin, either increasing or decreasing its effectiveness. The effects of warfarin are typically monitored by checking prothrombin time (INR) every one to four weeks.

Less common side effects may include areas of tissue damage, and purple toes syndrome. The common side effect, a natural consequence of reduced clotting, is bleeding. It is usually taken by mouth, but may also be administered intravenously.

Less commonly, it is used following ST-segment elevation myocardial infarction and orthopedic surgery. While the drug is described as a 'blood thinner', it does not reduce viscosity but inhibits coagulation, and is commonly used to prevent blood clots in the circulatory system such as deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who have atrial fibrillation, valvular heart disease, or artificial heart valves.

Subcutaneous administration should only be considered when a patient is unable to tolerate oral vitamin K therapy and is not clinically compromised enough to necessitate IV vitamin K 1.Warfarin is an anticoagulant used as a medication under several brand names including Coumadin, and as a poison for rats and other pests. Because intravenous (IV) administration of vitamin K 1 may be associated with anaphylactoid reactions, it should be avoided unless serious or life-threatening bleeding is present. 1 Oral administration of vitamin K 1 is safe and effective. The optimal dosage regimen of vitamin K 1 to treat patients who develop an elevated INR while receiving warfarin is given in the 2012 American College of Chest Physicians consensus guidelines. Acquired vitamin K deficiency typically results from the therapeutic administration of warfarin, or following the overdose of warfarin or a long-acting anticoagulant rodenticide (LAARs), such as brodifacoum. Vitamin K 1 (phytonadione) is the commercial preparation of the natural form of vitamin K (phylloquinone) that is indicated for the reversal of an elevated prothrombin time (PT) or an international normalized ratio (INR) in patients with xenobiotic induced vitamin K deficiency.

Inr antidote