Intramuscular Vitamin K Should Be Avoided in Adults with Elevated INR
Do not administer vitamin K intramuscularly to adults with elevated INR. The intramuscular route is contraindicated because it carries a risk of hematoma formation in anticoagulated patients and produces unpredictable pharmacologic responses that make it unsuitable for urgent or non-urgent reversal. 1
Preferred Routes of Administration
Oral Route (First-Line for Non-Bleeding Patients)
- Oral vitamin K is the preferred route for non-emergent reversal because it achieves predictable effectiveness with 95% of patients showing INR reduction within 24 hours, avoids injection-site hematomas, and eliminates the anaphylactic risk associated with rapid IV administration. 1
- For INR 5.0–9.0 without bleeding and high-risk factors (age >65–75 years, prior bleeding, concurrent antiplatelet therapy, renal failure, or alcohol use), administer oral vitamin K 1–2.5 mg. 1, 2
- For INR >10 without bleeding, give oral vitamin K 2.5–5 mg and recheck INR within 24 hours. 1, 2
Intravenous Route (For Major or Life-Threatening Bleeding)
- Intravenous administration is the only acceptable parenteral route when rapid reversal is required, achieving predictable INR reduction within 4–6 hours compared to 18–24 hours for oral dosing. 1
- For major bleeding, administer vitamin K 5–10 mg IV by slow infusion over 15–30 minutes, never exceeding 1 mg per minute to minimize anaphylactoid reactions (which occur in 3 per 100,000 doses). 1, 2, 3
- For life-threatening bleeding, combine vitamin K 5–10 mg IV with 4-factor prothrombin complex concentrate (PCC) 25–50 U/kg IV based on INR level, targeting INR <1.5. 1, 2
Why Subcutaneous and Intramuscular Routes Are Contraindicated
- Subcutaneous administration yields unpredictable pharmacologic responses with variable and sometimes delayed INR correction, making it unreliable for urgent warfarin reversal. 1
- Intramuscular injection is explicitly not recommended because anticoagulated patients are at high risk for injection-site hematomas, and the absorption is as unpredictable as the subcutaneous route. 1
Critical Dosing Algorithm Based on Clinical Scenario
| Clinical Scenario | Vitamin K Dose & Route | Additional Therapy | Target INR |
|---|---|---|---|
| INR 5.0–9.0, no bleeding, high-risk factors | 1–2.5 mg oral [1,2] | Withhold warfarin 1–2 doses [1] | <4.0 within 24 hr |
| INR >10, no bleeding | 2.5–5 mg oral [1,2] | Withhold warfarin [1] | <5.0 within 24 hr |
| Major bleeding (any INR) | 5–10 mg IV over 15–30 min [1,2] | Consider PCC if critical site or unstable [1] | <1.5 if life-threatening |
| Life-threatening bleeding (any INR) | 10 mg IV over 15–30 min [1,3] | PCC 25–50 U/kg IV (mandatory) [1,2] | <1.5 |
Common Pitfalls to Avoid
- Never use IM or subcutaneous routes for vitamin K administration in anticoagulated patients due to hematoma risk and unpredictable absorption. 1
- Do not exceed 10 mg vitamin K, as higher doses create a prothrombotic state and cause warfarin resistance lasting up to one week, requiring heparin bridging for re-anticoagulation. 1, 3
- Never rely on vitamin K monotherapy for major bleeding, as it cannot achieve the rapid hemostatic correction required; always pair it with 4-factor PCC when urgent reversal is needed. 1, 2
- Avoid rapid IV bolus administration; always dilute in 25–50 mL normal saline and infuse over 15–30 minutes to prevent anaphylactoid reactions. 1
Special Considerations for Mechanical Heart Valves
- In patients with mechanical prosthetic valves and elevated INR, use low-dose oral vitamin K (1–2 mg) to avoid excessively rapid INR correction, which increases the risk of valve thrombosis. 1, 2
- Consider bridging anticoagulation once bleeding is controlled in mechanical valve patients who require prolonged warfarin interruption. 2