Should a dose adjustment of warfarin (anticoagulant medication) be made for a patient with an International Normalized Ratio (INR) result of 1.93, which is below the target range of 2.0-3.0?

Warfarin Dose Adjustment for INR 1.93

Yes, you should increase the warfarin dose because an INR of 1.93 is below the standard therapeutic target range of 2.0-3.0, placing the patient at increased risk for thromboembolic events. 1, 2

Rationale for Dose Adjustment

• The FDA-approved target INR range for warfarin therapy is 2.0-3.0 for most indications including venous thromboembolism and atrial fibrillation, and your patient's INR of 1.93 falls below this therapeutic threshold 2
• The risk of thromboembolism is significantly greater when INR is <2.0, making subtherapeutic anticoagulation a more immediate concern than bleeding risk at this level 3
• The 2024 ESC Guidelines emphasize keeping INR in the 2.0-3.0 range for >70% of the time to maximize efficacy and safety 1

Specific Dosing Algorithm

Increase the total weekly warfarin dose by 10-20% rather than making dramatic changes, as most dose adjustments should alter the weekly dose by 5-20% 4

For example:

• If current dose is 5 mg daily (35 mg/week), increase to 5.5-6 mg daily (38.5-42 mg/week)
• If current dose is 7.5 mg daily (52.5 mg/week), increase to 8-9 mg daily (56-63 mg/week)

Do not make excessive dose increases: A single INR slightly out of range (within 0.5 units of target) might not require adjustment, but 1.93 is sufficiently below 2.0 to warrant intervention 1, 4

Monitoring Strategy

• Recheck INR within 3-7 days after dose adjustment to assess response 4
• Once INR stabilizes in the 2.0-3.0 range, gradually extend monitoring intervals from weekly to every 2-4 weeks, up to a maximum of 4-6 weeks for stable patients 1, 4

Investigation of Underlying Causes

Before adjusting the dose, identify factors that may have caused INR to drift below target 5:

• Dietary changes: Increased vitamin K intake from dark green vegetables, broccoli, soybeans, pickles, lettuce, or cooking oils (canola oil contains 141 μg vitamin K/100g) 1
• New medications: Drug interactions that reduce warfarin effect
• Decreased oral intake or illness: Affecting warfarin absorption
• Medication non-adherence: Missed doses
• Weight changes: Affecting volume of distribution

Common Pitfalls to Avoid

• Do not simply continue the same dose: An INR of 1.93 represents inadequate anticoagulation and requires intervention 5
• Do not use vitamin K: Vitamin K is only indicated for elevated INR (>5.0 without bleeding or any level with active bleeding), not for subtherapeutic levels 3
• Do not make 50% dose increases: Excessive adjustments will likely overshoot the target and cause supratherapeutic INR 5
• Do not delay adjustment: The patient remains at increased thromboembolic risk until INR reaches therapeutic range 6

Clinical Context Considerations

The specific indication for anticoagulation matters for target INR 2:

• Venous thromboembolism and atrial fibrillation: Target INR 2.0-3.0 (most common)
• Mechanical heart valves: May require higher target INR 2.5-3.5 depending on valve type 6
• Post-cardiac surgery patients: May initially target lower INR 1.5-2.6 until pericardial wires removed, but this is a temporary exception 7