Vitamin K (Phytonadione): Nursing

Vitamin K (phytonadione) is a fat-soluble vitamin essential for clotting and the specific antidote to warfarin. This note reviews its mechanism, indications, safe administration, interactions, and the nursing priorities most likely to appear on exams.

Mnemonic: "K for Koagulation (Clotting)."

Quick Reference Table

Indication	Mechanism	Key Exam Clue
Warfarin antidote	Reverses elevated INR	Not immediate — takes 6–24 hours to synthesize new clotting factors
Neonatal prophylaxis	Prevents vitamin K deficiency bleeding	Given IM in the vastus lateralis within 1 hour of birth
Dietary sources	Supports synthesis of clotting factors	Found in green leafy vegetables (spinach, kale)

Mechanism and Indications

Vitamin K is a fat-soluble vitamin essential for hepatic synthesis of clotting factors II, VII, IX, and X.
Acts as the specific antagonist to warfarin; used when INR is dangerously elevated or active bleeding occurs.
Newborns are born with a sterile gut and lack the bacteria needed to synthesize vitamin K, placing them at risk for hemorrhagic disease of the newborn.
Patients with biliary obstruction or malabsorption may become deficient because vitamin K absorption requires bile.

Administration and Safety

Oral route is preferred for non-emergency warfarin reversal.
Subcutaneous route has unpredictable absorption and is generally avoided.
IV route is reserved for emergency hemorrhage and requires extreme caution:
- Infuse slowly over 30–60 minutes.
- Rapid IV push can cause a severe anaphylactoid reaction (flushing, hypotension, cardiac arrest).
IM route is the standard for newborns (vastus lateralis) but should be avoided in adults with a high INR due to risk of hematoma formation.

Drug and Food Interactions

Patients on warfarin should not avoid vitamin K foods — they must maintain consistent dietary intake.
A sudden increase in green leafy vegetables will decrease warfarin's effectiveness and lower the INR.
Broad-spectrum antibiotics can kill vitamin K–producing gut bacteria, increasing bleeding risk.
Bile acid sequestrants decrease overall vitamin K absorption.

Monitoring and Nursing Care

Monitor PT (prothrombin time) and INR to evaluate treatment effectiveness.
Assess for signs of bleeding (e.g., hematuria, gingival bleeding, bruising) before and after administration.
Educate the patient that vitamin K does not work instantly — the liver needs hours to manufacture new clotting factors.
For life-threatening bleeding requiring immediate reversal, the provider may order Fresh Frozen Plasma (FFP) or Prothrombin Complex Concentrate (PCC).

Common Exam Traps

Assuming IV vitamin K can be given as a rapid push — it must be diluted and infused slowly.
Misreading the word "avoid" — the correct concept for dietary vitamin K is consistency, not avoidance.
Forgetting that the only acceptable injection site for an infant is the vastus lateralis.
Assuming vitamin K works as quickly as protamine sulfate — it does not, because it requires hepatic synthesis of new clotting factors.

Key Takeaways

Vitamin K is the antidote for warfarin and is required to synthesize clotting factors II, VII, IX, and X.
Onset is delayed (6–24 hours) — use FFP or PCC for immediate, life-threatening reversal.
Give IM in the vastus lateralis within 1 hour of birth for neonatal prophylaxis.
Infuse IV vitamin K slowly (30–60 minutes) to prevent anaphylactoid reactions.
Teach warfarin patients dietary consistency, not avoidance, of vitamin K–rich foods.
Always evaluate effectiveness by trending the INR and monitoring for active bleeding.

Vitamin K (Phytonadione): Nursing Pharmacology Study Guide