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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

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

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 →

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

Educational reference only

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.

Educational reference only

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.

Educational reference only

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

Plumb's Veterinary Drug Handbook
Withrow & MacEwen's Small Animal Clinical Oncology
Merck Veterinary Manual
NRC Nutrient Requirements of Dogs and Cats
Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

ASPCA Animal Poison Control Center Guidelines
AAHA Diabetes Management Guidelines
ASPCA Poison Control Guidelines
RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

EPIC Study (J Vet Intern Med 2016)
JVIM FAT CAT Study

Regulatory & approvals — 1

CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

Washington State University VCPL MDR1 Database