How to manage warfarin (Coumadin) therapy?

Warfarin (Coumadin) Management Protocol

Warfarin therapy must be individualized based on INR monitoring with a target INR of 2.0-3.0 for most conditions to minimize mortality and bleeding complications. 1, 2

Initial Dosing

• Starting dose:

  • Standard outpatient initiation: 5 mg daily (avoid 10 mg loading doses that can raise INR excessively) 3
  • For elderly patients (>75 years): Use lower initial doses of 2-4 mg 3
  • Begin warfarin on day 1-2 of heparin therapy when transitioning from parenteral anticoagulation 1

• Maintenance dosing:

  • Adjust based on INR monitoring
  • Expected maintenance dose: approximately 5 mg daily for warfarin 1
  • Dose adjustments should alter total weekly dose by 5-20% 3

INR Monitoring Schedule

• Initial phase:

  • Monitor INR daily until therapeutic range achieved 1
  • Then 2-3 times weekly for first 2 weeks 1
  • Then weekly until stable 1

• Maintenance phase:

  • Once stable, can extend to every 4 weeks maximum 1
  • More frequent monitoring for medication changes, illness, or diet changes

Target INR Ranges

• Standard target: INR 2.0-3.0 for most indications 1, 2

  • Venous thromboembolism (DVT/PE)
  • Atrial fibrillation
  • Most mechanical heart valves (St. Jude bileaflet in aortic position)

• Higher target: INR 2.5-3.5 2

  • Certain mechanical heart valves
  • Recurrent thrombosis despite therapeutic INR

Duration of Therapy

• Venous thromboembolism: 2

  • First DVT/PE with transient risk factor: 3 months
  • First idiopathic DVT/PE: 6-12 months
  • Recurrent DVT/PE: indefinite therapy
  • With thrombophilia: 6-12 months to indefinite based on specific condition

• Atrial fibrillation: Long-term/indefinite therapy 2

Managing Elevated INR

1. INR above therapeutic range but <5.0: 1

   • Reduce dose or omit next dose
   • Resume at lower dose when INR approaches desired range

2. INR 5.0-9.0 without bleeding: 1

   • Omit 1-2 doses of warfarin
   • Restart at lower dose when INR in therapeutic range
   • If increased bleeding risk: omit dose and give vitamin K₁ 1-2.5 mg orally

3. INR >9.0 without significant bleeding: 1

   • Give vitamin K₁ 3-5 mg orally
   • Monitor INR every 24 hours
   • Repeat vitamin K as necessary

4. Serious bleeding or major overdose: 1

   • Vitamin K₁ 10 mg by slow IV infusion
   • Fresh frozen plasma or prothrombin complex concentrate
   • Additional doses of vitamin K₁ every 12 hours as needed

Special Considerations

• Elderly patients:

  • More prone to bleeding even with therapeutic INR 1
  • Consider lower starting doses (2-4 mg) 3
  • May require more frequent monitoring

• Pregnancy:

  • Warfarin is contraindicated during pregnancy (Category X) 2
  • Replace with heparin during first trimester and last 6 weeks before delivery 1

• Drug interactions:

  • Numerous medications affect warfarin metabolism
  • Advise patients to consult before starting any new medication
  • Avoid NSAIDs and high-dose aspirin due to increased bleeding risk 1

• Diet:

  • Maintain consistent vitamin K intake
  • Avoid drastic changes in diet, especially green leafy vegetables
  • Avoid cranberry juice/products 2

Patient Education

• Strict adherence to prescribed dosage
• Report any unusual bleeding or bruising
• Avoid alcohol consumption
• Carry medical identification
• Take missed doses as soon as possible on same day, but never double dose
• Report illness, especially with fever or diarrhea
• Avoid activities with high risk of trauma 2

Common Pitfalls to Avoid

1. Loading with high doses - can cause excessive anticoagulation and bleeding risk
2. Infrequent INR monitoring - especially during initiation or dose changes
3. Failure to adjust for age - elderly patients typically need lower doses
4. Not accounting for drug interactions - many medications affect warfarin metabolism
5. Ignoring dietary changes - vitamin K intake should remain consistent