Vitamin K (Phytonadione)
Key Points
- Vitamin K (phytonadione) is the specific antidote and reversal agent for warfarin (and vitamin K deficiency–related bleeding).
- Warfarin inhibits vitamin K–dependent clotting factors II, VII, IX, and X; vitamin K restores their production.
- Intravenous vitamin K reverses warfarin’s anticoagulant effect within 1–2 hours; oral vitamin K acts within 6–10 hours.
- Therapeutic INR for most warfarin indications is 2.0–3.0; clients with mechanical heart valves target INR 2.5–3.5.
- Warfarin is contraindicated in pregnancy except for clients with mechanical heart valves; vitamin K must not be confused with potassium (both abbreviated “K”).
Mechanism of Action
Vitamin K (phytonadione) is a fat-soluble vitamin essential for the hepatic synthesis of clotting factors II (prothrombin), VII, IX, and X, as well as anticoagulant proteins C and S. Warfarin exerts its anticoagulant effect by inhibiting vitamin K epoxide reductase — the enzyme that recycles vitamin K to its active form — thereby reducing the production of these vitamin K–dependent clotting factors.
When phytonadione is administered, it replenishes active vitamin K, restoring hepatic synthesis of the affected clotting factors and reversing the anticoagulant effect of warfarin.
Indications
- Warfarin reversal: Supratherapeutic INR or active bleeding in a client on warfarin therapy
- Vitamin K deficiency bleeding (VKDB): Hemorrhagic disease of the newborn; routinely administered to neonates at birth
- Vitamin K deficiency in adults: Malabsorption syndromes, prolonged antibiotic use, or inadequate dietary intake
Dosing and Route
| Route | Onset of Effect | Clinical Use |
|---|---|---|
| Intravenous (IV) | 1–2 hours | Urgent or active bleeding requiring rapid reversal |
| Oral | 6–10 hours | Non-urgent supratherapeutic INR without active bleeding |
| Subcutaneous | Intermediate | Less predictable absorption than IV; generally avoided |
- Dose is titrated to the degree of INR elevation and clinical urgency; higher doses are used for significantly elevated INR.
- Caution: high doses can make re-anticoagulation with warfarin difficult in clients who require ongoing therapy.
- Fresh frozen plasma (FFP) may be co-administered for immediate reversal when urgent reduction of INR is needed, as vitamin K requires hepatic synthesis time even via IV route.
Nursing Assessment
NCLEX Focus
Know the difference between the onset of IV versus oral phytonadione, and understand when each route is clinically appropriate — this is a high-yield NCLEX distinction.
- Monitor INR before and after vitamin K administration; INR is the primary parameter guiding warfarin dosing and reversal.
- Assess for active bleeding: melena or hematochezia (GI bleeding), hematuria, epistaxis, gingival bleeding, intracranial bleeding signs (severe headache, altered mental status), or excessive bruising.
- Review current warfarin dose, INR trend, and indication for anticoagulation before administering reversal therapy.
- Assess dietary vitamin K intake: consistent intake of leafy green vegetables is recommended for clients on warfarin — sudden increases or reductions alter anticoagulant effect.
Nursing Interventions
- Administer IV phytonadione slowly (over at least 10–15 minutes) to minimize risk of anaphylactoid reactions, which can occur with rapid IV infusion.
- Do NOT confuse vitamin K with potassium — both are abbreviated “K.” Verify the order and drug name carefully before administration.
- Recheck INR at the appropriate interval following administration (1–2 hours post-IV or 6–10 hours post-oral) to evaluate effectiveness.
- Instruct clients on warfarin to maintain a consistent (not necessarily restricted) dietary intake of vitamin K — abrupt changes in consumption of high-vitamin K foods (kale, spinach, broccoli, brussels sprouts, collard greens) can destabilize INR.
- Educate clients on warfarin to notify all providers (including dentists) of anticoagulation status before any procedure; wear a medical alert bracelet; use electric razors and soft-bristle toothbrushes; and avoid alcohol, cranberries, and grapefruit.
Key Contraindications and Precautions
- Pregnancy: Warfarin is contraindicated in pregnancy due to fetal harm risk — vitamin K does not resolve this contraindication. Exception: clients with mechanical heart valves may require continued anticoagulation with careful risk-benefit assessment.
- Warfarin re-anticoagulation difficulty: Large doses of vitamin K can create sustained resistance to warfarin for days to weeks — dose conservatively when re-anticoagulation will be required.
- Active hemorrhage: Vitamin K alone is insufficient for acute life-threatening bleeding — FFP, prothrombin complex concentrate (PCC), or factor VII concentrate may be required in conjunction.
Related Concepts
- anticoagulants — Warfarin and the class of anticoagulant medications for which vitamin K serves as a reversal agent.
- hemostasis-coagulation-and-fibrinolysis — The coagulation cascade and the role of vitamin K–dependent factors.
- blood-transfusion-verification-initiation-and-reaction-response — Fresh frozen plasma as a co-intervention with vitamin K for acute warfarin reversal.
- medication-administration-safety-measures — Risk of dangerous drug name confusion between vitamin K and potassium.
- postpartum-hemorrhage — Phytonadione and hemorrhage management in the postpartum setting.
Self-Check
- A client on warfarin presents with an INR of 8.5 and mild gingival bleeding. What route of vitamin K administration would the nurse anticipate, and what is the expected onset?
- Why does the nurse need to be especially careful when administering intravenous vitamin K, and how should it be given to minimize adverse reactions?
- A client asks if they need to avoid all green vegetables because they are taking warfarin. How should the nurse respond?