Section 13 · Monograph
Phytonadione (vitamin K)
Reviewed Nov 2026FDA label
Mephyton / genericVitamin
- Forms
- Tab: 5mg | Inj: 10mg/mL
- Dose
- Warfarin reversal with PCC: 5-10mg slow IV (boxed warning: IV anaphylaxis risk)
- MOA
- Cofactor for hepatic synthesis of factors II, VII, IX, X
Black Box Warning
- Injectable: severe hypersensitivity reactions, including anaphylactoid reactions and deaths, have occurred with IV and IM use — restrict IV/IM to situations where the subcutaneous route is not feasible and the serious risk is justified
Indications
- Anticoagulant-induced prothrombin deficiency (warfarin)FDA-labeled
- Hypoprothrombinemia and vitamin K deficiency bleedingFDA-labeled
- Prophylaxis and treatment of hemorrhagic disease of the newbornFDA-labeled
Mechanism of Action
- Cofactor for gamma-glutamyl carboxylase; restores hepatic synthesis of factors II, VII, IX, X and proteins C and S
Full Dosing
Adult / usual
- Non-urgent warfarin reversal (elevated INR without major bleeding): 1-2.5mg orally
- Major bleeding with PCC: 5-10mg by slow IV infusion (no faster than 1mg/min)
- Newborn prophylaxis: 0.5-1mg IM single dose
Contraindications
- Hypersensitivity to phytonadione or injection components (polyoxyl castor oil in some products)
Drug Interactions
- Antagonizes warfarin — high doses can cause warfarin resistance when re-anticoagulating
- Orlistat, cholestyramine and mineral oil reduce absorption
- Antibiotics may reduce gut vitamin K production
Adverse Effects
- Hypersensitivity/anaphylactoid reactions with IV use
- Flushing, hypotension
- Injection-site reactions
- Delayed re-anticoagulation after reversal
Monitoring Parameters
- INR 6-12 hours after dose
- Bleeding signs
- Hypersensitivity monitoring during IV administration
Pregnancy & Lactation
- Used for newborn prophylaxis; vitamin K supplementation for mothers on enzyme-inducing antiepileptics is sometimes recommended late in pregnancy
- Compatible with breastfeeding