What is the recommended dose of vitamin K (phytonadione) for a patient with an elevated International Normalized Ratio (INR) of 8.98?

Vitamin K Dosing for INR of 8.98

For a patient with an INR of 8.98 without active bleeding, administer 2.5-5 mg of oral vitamin K (phytonadione) to safely reduce the INR within 24 hours. 1, 2

Assessment and Management Algorithm

For INR of 8.98 WITHOUT bleeding:

1. Initial management:

   • Omit the next 1-2 doses of warfarin 2
   • Administer 2.5-5 mg oral vitamin K (phytonadione) 1, 2
   • Recheck INR within 24 hours to ensure appropriate reduction 2

2. Expected response:

   • Oral vitamin K at this dose typically lowers INR within 24-48 hours 3
   • Studies show that oral vitamin K administration lowers INR more rapidly than simply holding warfarin 3

3. Route of administration:

   • Oral administration is preferred over intravenous due to risk of anaphylactoid reactions with IV administration 2, 4
   • Subcutaneous administration is less effective than oral or IV routes and should be avoided 5, 6

For INR of 8.98 WITH bleeding:

1. Minor bleeding:

   • Administer 2.5-5 mg oral vitamin K 2, 7
   • Monitor closely and recheck INR within 12-24 hours 2

2. Major bleeding:

   • Administer 5-10 mg vitamin K by slow intravenous infusion (over 30 minutes) 1, 3
   • Consider 4-factor prothrombin complex concentrate (PCC) as first-line therapy 8, 1
   • Hospital admission is recommended 2

3. Life-threatening bleeding:

   • Administer 10 mg intravenous vitamin K plus 4-factor PCC immediately 1, 3
   • Target INR < 1.5 for emergency interventions 1

Evidence Analysis

Oral vitamin K has been shown to be effective in managing excessive anticoagulation. A meta-analysis demonstrated that oral and intravenous vitamin K are equivalent and more effective than simply withholding warfarin 6. In a randomized controlled trial comparing oral versus IV phytonadione, both routes showed similar efficacy at 24 hours, though IV administration provided more rapid correction 4.

Another randomized trial showed that patients receiving 2.5 mg oral vitamin K had their INR reduced to ≤4.0 approximately one day faster than those who simply had warfarin withheld 7.

Important Considerations and Pitfalls

• Avoid excessive correction: High doses of vitamin K may lower INR more than necessary and lead to warfarin resistance for up to a week 3
• Mechanical heart valves: For patients with mechanical heart valves and supratherapeutic INR (>5.0), the benefit of individualized treatment with oral vitamin K is uncertain 8
• Risk factors: Patient-specific factors increasing bleeding risk include age >65 years, history of stroke or GI bleeding, renal insufficiency, anemia, and concomitant use of drugs affecting platelet function 3
• Follow-up: Investigate the cause of elevated INR (drug interactions, dietary changes, illness) to prevent recurrence 2
• Resumption of warfarin: If high-dose vitamin K was administered, bridging with heparin may be necessary until the patient becomes responsive to warfarin again 3

FDA Labeling Information

The FDA-approved dosing for phytonadione 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. Frequency and amount of subsequent doses should be determined by prothrombin time response or clinical condition 9.