From the Guidelines
For an elevated INR of 6, the recommended dose of vitamin K is typically 1-2.5 mg given orally, as this approach is appropriate for patients who are not actively bleeding and who are on warfarin therapy 1. The oral route is preferred because it provides a more predictable and gradual correction of the INR compared to intravenous administration, which can cause rapid reversal and potential thrombotic complications.
Key Considerations
- The effect of oral vitamin K begins within 24 hours, with maximum effect at 24-48 hours.
- If the patient is at higher risk of bleeding or has minor bleeding, a dose of 2.5-5 mg orally may be considered.
- For patients with serious or life-threatening bleeding, higher doses (5-10 mg) given intravenously would be appropriate, along with prothrombin complex concentrate or fresh frozen plasma 1.
Monitoring and Adjustment
- After administering vitamin K, the INR should be rechecked within 24-48 hours to ensure appropriate correction.
- Warfarin dosing should be adjusted accordingly to maintain a therapeutic INR range.
Mechanism of Action
- Vitamin K works by promoting the hepatic synthesis of clotting factors II, VII, IX, and X, which are inhibited by warfarin. It's essential to note that the management of elevated INR should be individualized, taking into account the patient's underlying condition, risk of bleeding, and risk of thromboembolism 1.
From the FDA Drug Label
The recommended dose to correct excessively prolonged prothrombin times caused by oral anticoagulant therapy is, 2.5 mg to 10 mg or up to 25 mg initially. In some instances 50 mg may be required. Evaluate INR after 6 to 8 hours, and repeat dose if INR remains prolonged. Modify subsequent dosage (amount and frequency) based upon the INR or clinical condition.
For an INR of 6, the recommended dose of vitamin K is 2.5 mg to 10 mg or up to 25 mg initially. The dose may be repeated if the INR remains prolonged after 6 to 8 hours, with subsequent dosage modified based on the INR or clinical condition. In some instances, a dose of up to 50 mg may be required 2.
From the Research
Vitamin K Dosage for Elevated INR
To manage an elevated International Normalized Ratio (INR) of 6, the appropriate dose of vitamin K can be considered based on the available evidence.
- The study 3 suggests that for moderately excessive baseline INR (6-10), a single dose of intravenous vitamin K (0.5 mg) can effectively reduce the INR, with 88% of patients responding within the first 12 hours.
- Another study 4 recommends a 1.0-mg vitamin K dose for patients with INR values between 4.5 and 10, as it is likely the most appropriate dose for this range.
- Additionally, the study 5 found that low-dose oral vitamin K (2 mg) effectively returns an INR between 4.5 and 10.0 to an INR of 2.0-3.0 within 24 hours in about 70% of patients.
- It is also worth noting that the study 6 used a single 2.5 mg dose of oral vitamin K to treat INR values of more than 10, but this may be higher than necessary for an INR of 6.
Considerations for Vitamin K Administration
When administering vitamin K, the route of administration and dose should be considered.
- Oral vitamin K is more effective than subcutaneous vitamin K injection and as effective as intravenous administration when INR values are compared 24 hours after administration 4.
- The fear of over-correction of the INR has limited the widespread use of vitamin K, but this occurs infrequently when small doses are administered orally 4.
Summary of Recommendations
Based on the available evidence, a dose of 0.5-1.0 mg of vitamin K may be considered for an INR of 6, depending on the route of administration and individual patient factors 3, 4. However, it is essential to consult with a healthcare professional to determine the most appropriate dose and treatment plan for each patient.