What is warfarin used for?

Warfarin Indications and Uses

Warfarin is primarily used as an anticoagulant for the prevention and treatment of thromboembolic disorders including venous thrombosis, pulmonary embolism, and thromboembolic complications associated with atrial fibrillation and cardiac valve replacement. 1

Primary Indications

Venous Thromboembolism

• Prevention of Venous Thrombosis: Warfarin is indicated for primary and secondary prevention of venous thromboembolism during hip surgery, total knee replacement, and major gynecologic surgery, typically with a target INR of 2.0-3.0 2
• Treatment of Deep Vein Thrombosis (DVT): Indicated for treatment of proximal venous thrombosis and symptomatic calf vein thrombosis with a recommended INR of 2.0-3.0 2
• Treatment of Pulmonary Embolism (PE): Used for treating pulmonary embolism with a recommended treatment duration of 6 months and target INR of 2.0-3.0 2

Cardiac Conditions

• Atrial Fibrillation: Prevents systemic embolism and stroke in patients with nonvalvular atrial fibrillation, with a target INR of 2.0-3.0 2
• Mechanical Heart Valves: Required for patients with mechanical prosthetic heart valves with a target INR of 2.5-3.5 2
• Bioprosthetic Valves: Recommended for the first 3 months after insertion of bioprosthetic valves in the mitral or aortic position with a target INR of 2.0-3.0 2
• Post-Myocardial Infarction: Reduces risk of death, recurrent myocardial infarction, and thromboembolic events such as stroke after myocardial infarction 1, 2
• Dilated Cardiomyopathy: Recommended for patients with an ejection fraction less than 25% with a target INR of 2.0-3.0 2

Other Indications

• Valvular Heart Disease: Indicated for patients with rheumatic mitral valvular disease with prior systemic embolization, paroxysmal or chronic atrial fibrillation, or left atrial diameter greater than 5.5 cm 2
• Patent Foramen Ovale with Atrial Septal Aneurysm: Indicated in patients with ischemic stroke of unknown origin who have this combination 2
• Recurrent Systemic Thromboembolism: Long-term anticoagulation (INR 2.0-3.0) is indicated in patients who have sustained one or more episodes of systemic thromboembolism 2

Duration of Therapy

• Symptomatic Calf Vein Thrombosis: 6-12 weeks 2
• Proximal DVT after Surgery/Medical Illness: 3-6 months 2, 3
• Idiopathic Proximal DVT: 6 months or longer 2, 3
• Pulmonary Embolism: 6 months recommended 2
• Recurrent Venous Thrombosis: Indefinite therapy should be considered 2, 3

Monitoring and Management

• Target INR Range: Most indications require an INR of 2.0-3.0, with mechanical heart valves requiring 2.5-3.5 2, 4
• Bleeding Risk: The risk of bleeding increases exponentially with INR and becomes clinically unacceptable once the INR exceeds 5.0 3
• Dose Adjustment: For subtherapeutic INR values, dose adjustments should be made with INR rechecking within 1 week 4
• Elderly Patients: May require lower warfarin doses due to increased sensitivity to anticoagulant effects 4

Important Considerations

• Drug Interactions: Numerous medications can significantly alter warfarin metabolism and effect 4, 5
• Dietary Factors: Changes in vitamin K intake can influence INR values 4
• Monitoring Frequency: After dose adjustment, INR should be rechecked within 1 week; for stable patients, testing can eventually be extended to every 4 weeks 4
• Contraindications: Not currently indicated for patients with ischemic cerebrovascular disease without other risk factors 2

Special Populations

• Elderly Patients: The benefits of warfarin must be carefully weighed against bleeding risk, particularly in patients over 75 years with atrial fibrillation, where a lower target INR of 2.0-2.5 may be considered 3
• Patients with Congenital Heart Disease: Warfarin is recommended for those with atrial fibrillation/flutter, history of embolic stroke, or Fontan circulation with documented atrial thrombus 2