Intramuscular Vitamin K (Phytonadione): Indications and Dosing
Intramuscular vitamin K is indicated primarily for newborn hemorrhagic disease prophylaxis (0.5-1 mg within one hour of birth) and for reversal of warfarin-induced coagulopathy in adults (2.5-25 mg, up to 50 mg in severe cases), though the subcutaneous route is preferred when feasible in adults due to safety concerns. 1, 2
Newborn Prophylaxis
The single most critical indication for IM vitamin K is prevention of vitamin K deficiency bleeding (VKDB) in all newborns:
- Administer 0.5-1.0 mg IM within one hour of birth 1, 2, 3
- This is the gold standard and most reliable method to prevent early, classic, and late VKDB 1
- IM administration creates a depot effect, maintaining protective levels for at least 2 months, significantly longer than oral formulations which last only 3-4 weeks 4
- The prolonged efficacy results from vitamin K forming a viscous mass in muscle tissue that is slowly absorbed over many weeks 4
For treatment of active hemorrhagic disease of the newborn:
- Give 1 mg IM or subcutaneously 2
- Higher doses may be necessary if the mother received oral anticoagulants 2
- A prompt PT shortening within 2-4 hours confirms the diagnosis 1, 2
Special newborn populations requiring IM (not oral) administration: 3, 5
- Preterm infants (who require 10 μg/kg/day on parenteral nutrition) 1, 6
- Infants with cholestasis or impaired intestinal absorption 3
- Infants too unwell to take oral vitamin K 3
- Infants whose mothers took medications interfering with vitamin K metabolism 3
Adult Indications
For warfarin reversal with major or life-threatening bleeding:
- Initial dose: 2.5-10 mg, up to 25 mg initially; rarely 50 mg may be required 2
- Must be given with prothrombin complex concentrate (PCC) 25 IU/kg for rapid reversal 7
- Vitamin K is essential because factor VII has a short half-life (6 hours); give 5-10 mg IV to maintain clotting factor levels after PCC wears off 7
- PCC reverses warfarin within 10-30 minutes, while vitamin K takes 6-12 hours IV or 24 hours orally to reach maximum effect 7, 6
- Check INR 30 minutes after PCC dosing; repeat dosing guided by clinical and laboratory assessment 7
For elevated INR without major bleeding:
- 2.5-10 mg is the typical range 2
- If PT not shortened satisfactorily in 6-8 hours, repeat the dose 2
- Oral and IV routes show similar efficacy at 24 hours, though IV acts faster initially 8
For hypoprothrombinemia from other causes:
- Dose range: 2.5-25 mg or more (rarely up to 50 mg) 2
- Amount and route depend on severity and response 2
Route Selection and Safety
Critical safety consideration: Subcutaneous route is preferred over IM in adults when possible 2
- When IV or IM administration is unavoidable, inject very slowly, not exceeding 1 mg per minute 2
- The FDA label emphasizes avoiding IV/IM routes when possible due to risk of severe reactions 2
For emergency antidote stocking in hospitals:
- Stock 50-100 mg total per facility 7
- Initial dose should be IV (not exceeding 10 mg), with subsequent doses given orally 7
- For patients with elevated INR and active bleeding, also administer prothrombin complex concentrate 7
Common Pitfalls
- Do not give IV glucose to patients at risk of thiamine deficiency before administering thiamine, as this can precipitate Wernicke's encephalopathy 7
- Large vitamin E doses can exacerbate vitamin K deficiency and affect coagulation 7
- Benzyl alcohol preservatives are toxic to newborns; use preservative-free diluents 2
- Oral vitamin K prophylaxis in newborns requires strict compliance with multi-dose protocols and is less reliable than IM 3, 4
- Vitamin K administration may affect anticoagulant therapy response; monitor coagulation parameters 6