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# Phytomenadione (vitamin K1)

Vitamin K1 as a medicine. It lets the liver make working clotting factors again: it reverses warfarin and prevents bleeding in newborns.

Updated 2026-11-01

- Class: [Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/)
- Enzyme: Vitamin K-dependent gamma-glutamyl carboxylase (GGCX), which uses vitamin K as its cofactor
- ATC code: B02BA01
- WHO Model List of Essential Medicines

Also called: phytonadione, vitamin K1

✂**Vitamin K-dependent gamma-glutamyl carboxylase (GGCX), which uses vitamin K as its cofactor**Phytomenadione (vitamin K1)

ⓘ The figure shows human gamma-glutamyl carboxylase holding vitamin K1 hydroquinone (the active, reduced form of phytomenadione) and a piece of factor IX.

**Target in 3D:** Vitamin K-dependent gamma-glutamyl carboxylase (GGCX), which uses vitamin K as its cofactor. PDB structure 9BVK (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/9BVK) · Drag to rotate · pinch to zoom

## Mechanism of action

Vitamin K is the cofactor of gamma-glutamyl carboxylase, a liver enzyme that adds carboxyl groups to glutamic acid residues of factors II, VII, IX and X (and proteins C and S). Only carboxylated factors can bind calcium and work. Warfarin and vitamin K deficiency leave the factors unfinished; phytomenadione supplies vitamin K again, so the liver releases working factors. It is not a clotting agent itself and its effect is not immediate.

- Phytomenadione restores the liver's supply of vitamin K
- Gamma-glutamyl carboxylase finishes factors II, VII, IX and X
- Working factors are released into the blood over hours
- The INR falls and bleeding risk drops

## Pharmacokinetics

**Absorption**
Given by mouth or by injection; the injection is preferred under the skin.

**Distribution**
Concentrated in the liver at first; it crosses the placenta.

**Metabolism**
Little is known about its fate; almost no unchanged vitamin K appears in bile or urine.

**Onset and duration**
Not immediate: the INR improves over about 1 to 8 hours.

## Indications

- Bleeding risk or bleeding from coumarin anticoagulants such as warfarin (too high INR). [Anticoagulant poisoning (warfarin and superwarfarins) →](https://durgical.com/en/conditions/anticoagulant-poisoning/)
- Prevention and treatment of vitamin K deficiency bleeding in newborns. [Vitamin K deficiency bleeding of the newborn →](https://durgical.com/en/conditions/vitamin-k-deficiency-bleeding-of-the-newborn/)
- Low prothrombin from poor vitamin K absorption (obstructive jaundice, coeliac disease, intestinal resection, cystic fibrosis) or from antibiotics.

## Adverse effects

### Common

- Pain, swelling and tenderness at the injection site
- Flushing, sweating, dizziness, altered taste
- Skin reactions after injection, sometimes weeks or months later

### Serious (rare, important)

- Fatal hypersensitivity reactions and anaphylaxis with intravenous or intramuscular injection, even with the first dose
- Excessive correction can bring back the original clotting risk
- Haemolysis, jaundice and high bilirubin in newborns, especially premature, with overdose

## Contraindications

- Hypersensitivity to any component of the product

## Key interactions

**Warfarin and other coumarins**
Reverses their effect; large amounts can cause temporary resistance when the anticoagulant is restarted.

**Heparin**
No effect: phytomenadione does not reverse heparin.

**Direct oral anticoagulants (apixaban, rivaroxaban, dabigatran)**
No useful effect on their anticoagulant activity.

## What is monitored

- INR, repeated over the following hours
- Signs of bleeding
- Signs of anaphylaxis during and after intravenous use: blood pressure, breathing, skin

## Administration and safety

- The injection is given under the skin whenever possible; when the IV route cannot be avoided it is injected very slowly
- The emulsion is protected from light at all times
- Resuscitation equipment is at hand for intravenous use
- In serious bleeding it is combined with faster products (prothrombin complex concentrate or plasma), because it acts only after hours

## Nursing care

- Check the INR before and after giving it
- Watch closely for flushing, breathing difficulty, low blood pressure or chest pain during an IV injection
- In newborns, record the prophylactic dose given after birth
- Teach patients on warfarin that sudden changes in vitamin K-rich foods (green leafy vegetables) move the INR

## Pregnancy and breastfeeding

It crosses the placenta; when it is needed in pregnancy, a preservative-free product is preferred.

## Memory aid

K for Koagulation: vitamin K finishes factors 2, 7, 9 and 10 ("1972"), but slowly: think hours, not minutes.

## Test yourself

Think of the answer, then tap the question to see it.

## Which clotting factors need vitamin K, and what enzyme uses it?

Factors II, VII, IX and X (and proteins C and S); gamma-glutamyl carboxylase uses vitamin K to carboxylate them.

## Why is vitamin K alone not enough for life-threatening bleeding on warfarin?

The INR takes hours to improve because the liver must make new factors; prothrombin complex concentrate or plasma replace them faster.

## Which route of vitamin K injection carries the highest risk of severe hypersensitivity?

Intravenous (and intramuscular) injection; fatal anaphylaxis has occurred, so the subcutaneous route is preferred when possible.

## Does vitamin K reverse heparin?

No. Heparin acts through antithrombin, not through vitamin K; protamine is its antidote.

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## Related drugs

- [Warfarin](https://durgical.com/en/pharmacology/warfarin/)
- [Protamine sulfate](https://durgical.com/en/pharmacology/protamine-sulfate/)
- [Heparin](https://durgical.com/en/pharmacology/heparin/)

## Related conditions

- [Anticoagulant poisoning (warfarin and superwarfarins)](https://durgical.com/en/conditions/anticoagulant-poisoning/)
- [Vitamin K deficiency bleeding of the newborn](https://durgical.com/en/conditions/vitamin-k-deficiency-bleeding-of-the-newborn/)

[← Back to the class: Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - PHYTONADIONE injection, emulsion](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=226c0a5c-3e04-65a9-01ac-e67aad9a430a) (DailyMed (U.S. National Library of Medicine), 2026); [Phytonadione Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a626026.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Phytonadione: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682659.html) (MedlinePlus (U.S. National Library of Medicine), 2017); [9BVK: Vitamin K-dependent gamma-carboxylase with factor IX propeptide and glutamate-rich region and with vitamin K hydroquinone](https://www.rcsb.org/structure/9BVK) (RCSB Protein Data Bank, 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/phytomenadione/