What is the starting dose of warfarin (International Normalized Ratio (INR) anticoagulant) for Deep Vein Thrombosis (DVT)?

Starting Dose of Warfarin for DVT

For patients with deep vein thrombosis (DVT), warfarin should be initiated at 10 mg daily for the first 2 days followed by dosing based on INR measurements rather than starting with the estimated maintenance dose. 1

Initial Warfarin Dosing Protocol

The American College of Chest Physicians (ACCP) guidelines recommend the following approach for warfarin initiation in DVT patients:

• Standard outpatient protocol: 10 mg daily for the first 2 days, then adjust based on INR measurements 1
• Special populations requiring lower initial doses (5 mg or less):
  • Elderly patients
  • Debilitated patients
  • Patients with hepatic insufficiency
  • Patients with potential for greater than expected INR response 2

Overlap with Parenteral Anticoagulation

When initiating warfarin for DVT treatment, it must be overlapped with a parenteral anticoagulant:

• Continue parenteral anticoagulant (heparin, LMWH, or fondaparinux) for a minimum of 5 days 1
• Continue parenteral anticoagulant until the INR is ≥2.0 for at least 24 hours 1
• For cancer patients, LMWH monotherapy is preferred over transitioning to warfarin 1

INR Monitoring Schedule

• First INR check: Day 4 after warfarin initiation 2, 3
• Second INR check: Day 6 after warfarin initiation 2, 3
• Subsequent monitoring: Twice weekly until stable, then gradually decrease frequency 2

Target INR Range

• Standard target INR for DVT treatment: 2.0-3.0 1, 2
• Duration of therapy depends on risk factors and whether the DVT is provoked or unprovoked 1

Evidence Supporting 10 mg Starting Dose

The recommendation for a 10 mg starting dose is based on multiple studies showing:

• Faster achievement of therapeutic INR (4.2 days vs 5.6 days) 1
• Higher proportion of patients reaching therapeutic range by day 5 (86% vs 45%) 1
• Similar safety profile compared to lower starting doses 1

Common Pitfalls and Caveats

1. Avoid loading doses in high-risk patients: While 10 mg is recommended for most outpatients, lower doses (5 mg or less) should be used in elderly, debilitated patients, or those with hepatic dysfunction 2

2. Don't discontinue parenteral anticoagulation too early: Continue heparin/LMWH until INR is therapeutic for at least 24 hours to prevent recurrent thromboembolism 1

3. Monitor for drug interactions: Many medications can potentiate or inhibit warfarin's effect, requiring dose adjustments

4. Cancer patients require special consideration: LMWH monotherapy is preferred over warfarin for cancer-associated DVT 1

5. Outpatient vs inpatient protocols may differ: The 10 mg loading dose is specifically recommended for outpatients healthy enough for outpatient management 1

By following this evidence-based protocol for warfarin initiation in DVT patients, you can achieve therapeutic anticoagulation efficiently while minimizing the risk of complications.