What is the initial dose of Coumadin (warfarin) for patients with pulmonary embolism (PE)?

Initial Warfarin Dosing for Pulmonary Embolism

Start warfarin at 5-10 mg daily for the first 2 days, then adjust to maintain an INR of 2.0-3.0. 1

Starting Dose Recommendations

The FDA-approved dosing for warfarin in PE treatment is 2-5 mg per day as the initial dose, with adjustments based on PT/INR response. 2 However, the British Thoracic Society guidelines recommend a higher initial range of 5-10 mg daily for 2 days, followed by 1-10 mg daily thereafter. 1

For most patients, I recommend starting with 5 mg daily, which represents the middle ground between these recommendations and avoids the complications of loading doses while achieving therapeutic anticoagulation efficiently. 3

Key Dosing Considerations:

• Lower initial doses (2-4 mg) should be used for:

  • Elderly or debilitated patients 2
  • Patients with genetic variations in CYP2C9 and VKORC1 enzymes 2
  • Patients expected to have greater PT/INR sensitivity 2

• Avoid loading doses - they increase hemorrhagic complications without providing faster protection against thrombus formation 2, 3

Concurrent Heparin Therapy

Warfarin must be started simultaneously with therapeutic heparin anticoagulation, not as monotherapy. 1, 4, 5

• Begin heparin immediately (bolus of 80 IU/kg IV, then 18 IU/kg/hour infusion) 1, 6, 4
• Target aPTT of 1.5-2.5 times control (45-75 seconds) 1, 6, 4
• Continue heparin for at least 5 days AND until INR ≥2.0 on two measurements at least 24 hours apart 1, 6, 5

INR Monitoring Protocol

• Target INR: 2.0-3.0 for all PE patients 1, 2
• Check INR daily after starting warfarin until stable in therapeutic range 2
• Once stable, gradually extend monitoring intervals up to 1-4 weeks 2
• Adjust subsequent doses by 5-20% of the total weekly dose based on INR results 3

Duration of Therapy

The duration depends on PE etiology: 2

• First episode with transient risk factor: 3 months 2
• First idiopathic PE: 6-12 months minimum 2
• Recurrent PE (≥2 episodes): Indefinite therapy 2
• Thrombophilic conditions: 12 months to indefinite 2

Common Pitfalls to Avoid

• Never use warfarin as monotherapy initially - always bridge with heparin to prevent paradoxical thrombosis from early protein C/S depletion 5
• Don't discontinue heparin prematurely - must overlap for minimum 4-5 days even if INR reaches 2.0 earlier 1, 5
• Avoid excessive initial doses - a 5 mg starting dose will not raise INR appreciably in the first 24 hours, which is expected and appropriate 3
• Don't adjust dose for single slightly out-of-range INR - wait for trend confirmation unless significantly elevated 3