How to switch an adult patient with a history of thromboembolic events and normal renal and liver function from heparin (unfractionated heparin) 5000 units three times a day to coumadin (warfarin)?

Transitioning from Prophylactic Heparin to Warfarin

For a patient currently on prophylactic-dose unfractionated heparin (5000 units three times daily), you should start warfarin immediately while continuing the heparin, overlap both agents for at least 4-5 days, and discontinue heparin only after the INR has been therapeutic (2.0-3.0) for at least 24 hours on two consecutive measurements. 1

Critical Context: Prophylactic vs. Therapeutic Dosing

The dose you describe (5000 units three times daily) is prophylactic dosing, not therapeutic anticoagulation for active thromboembolism. 2 This is a crucial distinction that affects the transition strategy:

• If this patient has had a thromboembolic event (DVT, PE, or other), they require full therapeutic anticoagulation, not prophylaxis. 2
• If this is purely prophylactic (no active clot), the indication for warfarin should be carefully reconsidered, as prophylactic heparin is typically used short-term in hospitalized patients. 3, 4

Transition Protocol for Active Thromboembolism

Step 1: Initiate Warfarin Immediately

• Start warfarin on day 1 at the estimated patient-specific maintenance dose (typically 5 mg daily for most adults, adjusted for age, body size, and drug interactions). 1
• Do not use loading doses - they increase bleeding risk without accelerating therapeutic anticoagulation. 1, 5

Step 2: Overlap Therapy

• Continue full-dose heparin during the overlap period. 1
• The current prophylactic dose (5000 units TID) is inadequate for treating active thromboembolism. 2, 5
• For therapeutic anticoagulation, you need either:
  • IV heparin: 80 units/kg bolus, then 18 units/kg/hour infusion (or 5000 unit bolus followed by at least 32,000 units/24 hours) 2
  • Subcutaneous therapeutic heparin: 250 units/kg twice daily after initial 5000 unit IV bolus 2

Step 3: Monitor INR Timing

• Begin checking INR daily once warfarin is started. 1
• Critical timing for INR checks when on concurrent heparin: 1
  • At least 5 hours after last IV heparin bolus
  • At least 4 hours after stopping continuous IV heparin infusion
  • At least 24 hours after last subcutaneous heparin injection

Step 4: Discontinue Heparin

• Continue overlap for minimum 4-5 days AND until: 1, 5
  • INR is 2.0-3.0 on two measurements at least 24 hours apart 5
• Common pitfall: Stopping heparin too early (before day 4-5) even if INR is therapeutic, as warfarin's full anticoagulant effect requires depletion of all vitamin K-dependent factors. 1, 6

Special Considerations

If Patient Has Nephrotic Syndrome

• Higher heparin doses may be required due to antithrombin III urinary losses. 2
• Monitor INR more frequently as warfarin protein binding fluctuates with changing albumin levels. 2
• Target INR remains 2.0-3.0. 2

Monitoring Considerations

• Heparin can artificially elevate INR measurements, which is why timing of INR checks relative to heparin administration is critical. 1
• A severely elevated aPTT (>50 seconds) with therapeutic INR indicates increased bleeding risk. 1
• Watch for heparin-induced thrombocytopenia: check platelet counts every 2-3 days from day 4-14 if HIT risk ≥1%. 4

Common Pitfalls to Avoid

1. Using prophylactic heparin doses to treat active thromboembolism - this leads to 25% recurrence rates. 2, 6

2. Stopping heparin before adequate warfarin effect - warfarin initially creates a hypercoagulable state by depleting protein C before depleting clotting factors. 1, 5

3. Checking INR at wrong times - heparin interferes with INR measurement; follow the timing guidelines above. 1

4. Starting warfarin without confirming the indication - if the patient only needs short-term prophylaxis (e.g., post-surgical), warfarin may be unnecessary. 2, 3

5. Inadequate overlap duration - even with therapeutic INR, continue heparin for full 4-5 days minimum. 1, 5