coumadin

Coumadin is a brand name for warfarin, an oral anticoagulant used to prevent and treat blood clots. Warfarin works as a vitamin K antagonist, inhibiting the hepatic synthesis of vitamin K–dependent clotting factors II, VII, IX, and X, as well as regulatory proteins C and S. By reducing these factors, it decreases blood clotting and prolongs the prothrombin time, measured as the international normalized ratio (INR).

Indications for Coumadin include prevention of stroke in nonvalvular atrial fibrillation, treatment and prevention of deep vein thrombosis and pulmonary embolism, and prevention of thromboembolism in patients with mechanical heart valves. It is also used around certain surgical procedures to prevent clot formation.

Administration and monitoring involve taking warfarin orally with individualized dosing. Dosing is adjusted based on INR to attain target ranges that vary by condition, commonly around an INR of 2.0 to 3.0, with higher targets for some mechanical valves. Regular INR testing is required, especially after starting therapy or changing doses. Patients should maintain a consistent intake of vitamin K–containing foods, and clinicians may bridge therapy with heparin during initiation or around procedures.

Interactions and cautions: Warfarin interacts with many drugs and supplements; antibiotics, certain antifungals, and some antiarrhythmics can alter INR. NSAIDs and other antiplatelets increase bleeding risk. Contraindications include active major bleeding, significant bleeding disorders, severe liver disease, and pregnancy in most cases. Caution is advised in the elderly, malnourished individuals, or those with unstable health.

Adverse effects and overdose: The main risk is bleeding. Rare adverse effects include skin necrosis and purple toe syndrome. Overdose is treated with vitamin K and, for major bleeding, reversal products such as intravenous vitamin K and possibly plasma or coagulation factors. DOACs have reduced use in some settings, but warfarin remains essential for mechanical heart valves and certain conditions.