What adjustments should be made to the Coumadin (warfarin) dose for a patient with atrial fibrillation, history of pulmonary embolism, and DVT, taking 4 mg four days a week and 5 mg three days a week, with an INR of 1.55?

Warfarin Dose Adjustment for Subtherapeutic INR

Increase the total weekly warfarin dose by 10-20% to achieve the therapeutic INR target of 2.0-3.0, recheck INR in 1-2 weeks, and continue monitoring until stable therapeutic anticoagulation is achieved. 1

Current Clinical Situation

Your patient is significantly underanticoagulated with an INR of 1.55, placing them at high risk for thromboembolic events given their multiple indications for anticoagulation (atrial fibrillation, history of pulmonary embolism, and DVT). 2 An INR below 2.0 provides only approximately 80% of the stroke protection achieved with therapeutic anticoagulation (INR 2.0-3.0), representing inadequate protection. 1

Target INR Range

• The therapeutic INR target is 2.0-3.0 for all three of this patient's conditions (atrial fibrillation, pulmonary embolism history, and DVT history), with an optimal target of 2.5 within this range. 2, 3
• This target applies regardless of whether the atrial fibrillation is paroxysmal, persistent, or permanent. 2, 4
• For patients with history of venous thromboembolism (PE/DVT), the same INR range of 2.0-3.0 is recommended. 3

Specific Dose Adjustment

Current regimen: 4 mg × 4 days + 5 mg × 3 days = 31 mg/week

Recommended adjustment options:

• Increase total weekly dose by 10-15% (approximately 3-5 mg/week) to a total of 34-36 mg weekly. 1
• Practical approach: Change to 5 mg daily for 6 days and 6 mg for 1 day (total 36 mg/week), representing a 16% increase. 1
• Alternative: 5 mg daily for all 7 days (total 35 mg/week), representing a 13% increase.

The American College of Chest Physicians supports dose increases of 10-15% when INR is subtherapeutic. 1

Monitoring Schedule

• Recheck INR in 1-2 weeks after dose adjustment to assess response and ensure movement toward therapeutic range. 2, 1
• Once therapeutic INR is achieved, continue weekly INR monitoring until stable (defined as 2-3 consecutive therapeutic INR values). 2
• After stability is established, transition to monthly INR monitoring. 2
• The goal is to maintain time in therapeutic range (TTR) ≥65-70%, ideally ≥70%. 1, 4

Critical Considerations for This Patient

High thrombotic risk: This patient has multiple high-risk features for thromboembolism:

• Atrial fibrillation increases stroke risk 5-fold. 1
• History of both pulmonary embolism and DVT indicates recurrent venous thromboembolism, which warrants indefinite anticoagulation. 3
• Current subtherapeutic anticoagulation places them at immediate risk for recurrent events. 5

Evidence against low-intensity anticoagulation: While some studies in elderly patients (>65 years) suggest low-intensity INR (1.5-2.0) may reduce bleeding, meta-analysis demonstrates that adjusted-dose warfarin (INR 2.0-3.0) is significantly more effective at preventing thrombotic events (RR 0.50,95% CI 0.25-0.97) without statistically increasing major bleeding risk compared to low-dose therapy. 5 Given this patient's history of both PE and DVT, standard-intensity anticoagulation is essential. 3

Common Pitfalls to Avoid

• Do not use low-intensity INR targets (1.5-2.0) in patients with history of venous thromboembolism, as this provides inadequate protection. 5
• Avoid making dose adjustments >20% at one time, as this can lead to overshooting the therapeutic range. 1
• Do not wait longer than 2 weeks to recheck INR after dose adjustment in a patient with subtherapeutic anticoagulation and high thrombotic risk. 2
• Ensure patient adherence and assess for factors affecting warfarin metabolism (dietary vitamin K intake, new medications, intercurrent illness) before making dose changes. 2

Duration of Therapy

Given this patient's history of recurrent venous thromboembolism (both PE and DVT) plus atrial fibrillation, indefinite anticoagulation is indicated. 3 The FDA label specifically recommends indefinite warfarin therapy for patients with two or more episodes of documented DVT or PE. 3