Warfarin

Warfarin is an oral anticoagulant in the vitamin K antagonist class. It inhibits vitamin K epoxide reductase (VKORC1), reducing regeneration of active vitamin K and thereby lowering synthesis of the vitamin K–dependent coagulation factors II, VII, IX, and X, as well as proteins C and S. This shifts the hemostatic balance toward reduced clot formation.

Clinical use centers on prevention and treatment of thromboembolism. Indications include nonvalvular atrial fibrillation, venous thromboembolism (deep vein thrombosis and pulmonary embolism), and mechanical heart valves. It is often used with bridging heparin around surgical procedures or in long-term management of high‑risk thrombosis.

Dosing and monitoring require careful INR monitoring due to a narrow therapeutic index. Typical starting doses range from 2 to 5 mg daily, with adjustments based on the international normalized ratio (INR). Target INR varies by indication, commonly about 2.0–3.0 for many conditions; different valve patients may have higher targets. Once stable, patients are monitored at intervals determined by stability. Diet (notably vitamin K–rich foods) and numerous drug interactions can affect INR.

Reversal and safety: major bleeding is the principal risk. Reversal is with vitamin K, and in urgent cases with prothrombin complex concentrates or fresh frozen plasma. Ongoing care involves avoidance of unnecessary drug interactions, cautious use with NSAIDs and antibiotics, and patient education on signs of bleeding.

Contraindications include active major bleeding and pregnancy, given teratogenic risk. Warfarin has a long history, with brand names such as Coumadin and Jantoven. It remains an important, but carefully managed, anticoagulant in modern medicine.