What are the guidelines for daily management of Warfarin (anticoagulant) therapy?

Daily Management of Warfarin Therapy

Regular INR monitoring and dose adjustment are the cornerstones of safe and effective warfarin therapy, with the goal of maintaining the INR within the therapeutic range (typically 2.0-3.0) to minimize risks of thromboembolism and bleeding. 1

Initial Warfarin Dosing

• Start with 5 mg daily for most patients (avoid loading doses), which typically results in an INR of 2.0 after 4-5 days 1, 2
• Use lower starting doses (2-4 mg) in elderly patients, those at increased bleeding risk, or patients likely to be sensitive to warfarin 1, 2
• When rapid anticoagulation is required, administer heparin concurrently with warfarin for at least 4 days, continuing heparin until the INR has been in therapeutic range for 2 consecutive days 1
• For non-urgent anticoagulation (e.g., chronic atrial fibrillation), outpatient initiation with 4-5 mg daily typically produces a satisfactory anticoagulant effect within 6 days 1

INR Monitoring Schedule

• Check INR daily until therapeutic range is reached and sustained for 2 consecutive days 1
• Then check 2-3 times weekly for 1-2 weeks 1
• Then less frequently according to stability of results 1
• Once stable, INR monitoring can be reduced to intervals as long as 4 weeks 1
• Resume frequent monitoring when dose adjustments are required or when factors affecting warfarin metabolism change 1

Target INR Ranges

• Most indications (including venous thromboembolism, atrial fibrillation): INR 2.0-3.0 1, 3, 4
• Mechanical heart valves: INR 2.5-3.5 for mitral or combined mitral/aortic valves; INR 2.0-3.0 for bileaflet or tilting disc valves in aortic position 3, 5
• Post-myocardial infarction: Target INR 2.5 (range 2.0-3.0) with aspirin, or target INR 3.5 (range 3.0-4.0) without aspirin 3

Dose Adjustment Guidelines

• For INR within therapeutic range: continue current dose 1
• For INR above therapeutic range but <5 (without bleeding): reduce daily dose until INR returns to therapeutic range 1
• For INR >5: defer any procedures, contact anticoagulation clinic or medical practitioner for advice 1
• Most dose adjustments should alter the total weekly dose by 5-20% 2
• Single INR values slightly out of range may not require dose adjustment 2

Managing Elevated INR

• For INR 4.5-10.0 without bleeding: withholding warfarin with careful monitoring is generally safe 5
• For excessive INR with clinically important bleeding: administer clotting factors (e.g., fresh-frozen plasma) and vitamin K₁ 2
• For non-bleeding patient with INR >9: consider low-dose vitamin K₁ (e.g., 2.5 mg orally) 2
• When oral vitamin K₁ is used, the injectable formulation (given orally) is preferred 5

Perioperative Management

Low-Risk Procedures:

• Continue warfarin therapy 1
• Check INR during week before procedure to ensure it's within therapeutic range 1

High-Risk Procedures with Low Thrombotic Risk:

• Stop warfarin 5 days before procedure 1
• Check INR prior to procedure to ensure it's <1.5 1
• Restart warfarin with usual daily dose on the evening of the procedure 1
• Check INR one week later to ensure adequate anticoagulation 1

High-Risk Procedures with High Thrombotic Risk:

• Stop warfarin 5 days before procedure 1
• Start therapeutic dose LMWH two days after stopping warfarin 1
• Administer last dose of LMWH at least 24 hours before procedure 1
• Check INR prior to procedure to ensure it's <1.5 1
• Resume warfarin on the day of procedure with usual dose 1
• Restart therapeutic dose LMWH the day after procedure 1
• Continue LMWH until satisfactory INR is achieved 1

Special Considerations

• Advise all patients on warfarin that they have an increased risk of post-procedure bleeding compared to non-anticoagulated patients 1
• Factors increasing bleeding risk include: advanced age, history of bleeding, and comorbidities such as renal insufficiency or anemia 1
• Fluctuations in dose-response may occur due to changes in diet, concurrent medications, poor compliance, or alcohol consumption 1
• Point-of-care testing may be appropriate for some patients, allowing home monitoring 1
• For patients who have experienced bleeding during therapeutic warfarin therapy but require continued anticoagulation, consider lower target INR ranges (e.g., 2.0-2.5 for mechanical heart valves, 1.5-2.0 for atrial fibrillation) 1