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Phytonadione (Vitamin K1)

Prescription
Fat-Soluble Vitamin / Anticoagulant Antidote
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
3 available
Interactions
1 documented
Formulations
3

Mechanism of action

Essential cofactor for hepatic gamma-carboxylation of coagulation factors II, VII, IX, and X, and anticoagulant proteins C and S. Reverses anticoagulant rodenticide toxicity by replenishing functional vitamin K in the carboxylation cycle.

At a glance

Class
Fat-Soluble Vitamin / Anticoagulant Antidote
Schedule
Prescription
Storage
Store at 15–30°C; protect from light (light-sensitive); injectable stable at room temperature

Dosing

🐕

Dog

PO route most effective (fat-soluble — give with fatty meal)
Dose
1–2 mg/kg
Route
PO (preferred), SQ, IM, IV (last resort)
Frequency
q8–12h (PO)
🐈

Cat

Same as dogs
Dose
2.5–5 mg/kg
Route
PO, SQ
Frequency
q8–12h

Formulations

💊

Other — 3

Strength
—
Strength
—
Strength
—

Storage

Store at 15–30°C; protect from light (light-sensitive); injectable stable at room temperature

Safety

Monitoring parameters

PT/aPTT before treatment and 48h after stoppingClinical bleeding signs (hemoptysis, epistaxis, melena, hematoma)PCV/hematocrit

Interactions

Major — 1

Warfarin
major
Vitamin K1 directly antagonizes warfarin's mechanism of action (restores vitamin K-dependent clotting factor carboxylation). Used therapeutically as warfarin antidote, but also interferes with warfarin therapy.
Management: Intentional use as warfarin antidote for over-anticoagulation. If patient needs both anticoagulation and has dietary Vitamin K variation, maintain consistent Vitamin K intake.

Brands

Other markets

AquaMEPHYTON
Mephyton
Veta-K1

FAQs

Frequently asked questions

›What is Phytonadione (Vitamin K1)?
Phytonadione (Vitamin K1) is a fat-soluble vitamin / anticoagulant antidote used in pets. Essential cofactor for hepatic gamma-carboxylation of coagulation factors II, VII, IX, and X, and anticoagulant proteins C and S. Reverses anticoagulant rodenticide toxicity by replenishing functional vitamin K in the carboxylation cycle.
›What is Phytonadione (Vitamin K1) used for in pets?
Phytonadione (Vitamin K1) is used in veterinary medicine for: PO route most effective (fat-soluble — give with fatty meal); Same as dogs.
›What is the Phytonadione (Vitamin K1) dose for dogs?
For dogs, Phytonadione (Vitamin K1) is typically dosed as follows — PO route most effective (fat-soluble — give with fatty meal): 1–2 mg/kg PO (preferred)/SQ/IM/IV (last resort) q8–12h (PO). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Phytonadione (Vitamin K1) dose for cats?
For cats, Phytonadione (Vitamin K1) is typically dosed as follows — Same as dogs: 2.5–5 mg/kg PO/SQ q8–12h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Phytonadione (Vitamin K1) need a prescription?
Yes. Phytonadione (Vitamin K1) is a prescription medication and should only be administered under veterinary supervision.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →