Phytonadione (Vitamin K1): veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Vita-K, Mephyton, AquaMephyton

Species with doses

Dogs, Cats, Cattle, Horses, Goats, Sheep, Pigs, Birds, Rabbits and Small mammals

General dose range

0.25–5 mg/kg PO q12h × 2–4 weeks (rodenticide protocol) — check the species tables for the indication

Routes

PO, SC, IM

Last reviewed

1 October 2026

Indications

• Anticoagulant rodenticide toxicosis (first / second / third generation)
• Adjunctive therapy of acute liver failure
• Hereditary coagulation factor deficiency adjunct
• Bile obstruction → fat-soluble vitamin malabsorption (Vit K deficiency)
• Newborn ruminant haemorrhagic disease (sweet clover ingestion in dam)

Phytonadione (Vitamin K1) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Anticoagulant rodenticide — first generation: Plumb’s p.976 (Merola 2002): first-generation anticoagulants — 14 days of vitamin K1 is usually sufficient; 1.25–2.5 mg/kg PO twice daily with a fatty meal (Talcott 2008). Papich 5e: short-acting rodenticides 1 mg/kg/day SC or PO for 10–14 days. Check PT 48 h after the last dose.
• Anticoagulant rodenticide — second generation (brodifacoum): Plumb’s p.976: bleeding patients 2.5 mg/kg PO twice daily with a fatty meal for at least 4 weeks (Talcott 2008); second-generation or unknown anticoagulant — at least 30 days (Merola 2002). Papich 5e: long-acting rodenticides 2.5–5 mg/kg/day for 3–4 weeks. Recheck PT 48–72 h after stopping; continue another week if prolonged. Typical oral range 1.25–2.5 mg/kg q12h (Papich 5e: 2.5–5 mg/kg/day).
• Acutely bleeding patient — SC for rapid effect: Plumb’s p.976: oral dosing is preferred; give the starting dose SC only if the patient is vomiting or activated charcoal has been given. Never IV (anaphylaxis). Plasma transfusion is needed for active haemorrhage — vitamin K1 takes 6–12 h to act. Starting dose 1.25–2.5 mg/kg SC with small needles at several sites.

Cats

• Anticoagulant rodenticide: Plumb’s p.976 (dogs and cats): 1.25–2.5 mg/kg PO twice daily with a fatty meal — 14 days for first-generation, at least 30 days for second-generation or unknown agents. Papich 5e: 1 mg/kg/day for 10–14 days (short-acting) or 2.5–5 mg/kg/day for 3–4 weeks (long-acting).

Cattle

• Sweet clover poisoning (moulded dicoumarol): Plumb’s p.976 (Oehme 2009): sweet clover or lespedeza toxicity 1–1.5 mg/kg SC for several days; remove the source and avoid stress. WITHDRAWAL — Plumb’s: the labelled injection carries no withdrawal times.
• Anticoagulant rodenticide toxicity: Papich 5e and Plumb’s p.976 (Upson; Veda-K1 label): 0.5–2.5 mg/kg IM or SC. For acute haemorrhage IV only if essential — diluted, no faster than 10 mg/min in adults, 5 mg/min in young animals. Second-generation agents may need 3–4 weeks (Bailey 1986).

Horses

• Anticoagulant rodenticide: Papich 5e: horses 0.5–2.5 mg/kg SC or IM. Plumb’s p.976: 0.5–2.5 mg/kg IM (Upson 1988); 500 mg TOTAL SC q4–6h until prothrombin time returns to normal (Byars 1987). Avoid IV; if unavoidable, dilute and give no faster than 5 mg/min.

Goats

• Warfarin-type toxicity: Papich 5e and Plumb’s p.976 (Upson 1988): sheep and goats 0.5–2.5 mg/kg IM or SC; if IV is unavoidable, dilute and give no faster than 5 mg/min.

Sheep

• Warfarin-type toxicity: Papich 5e and Plumb’s p.976 (Upson 1988): sheep and goats 0.5–2.5 mg/kg IM or SC; if IV is unavoidable, dilute and give no faster than 5 mg/min.

Pigs

• Warfarin-type toxicity: Plumb’s p.976 (Upson 1988): swine 0.5–2.5 mg/kg IM; if IV is unavoidable, dilute and give no faster than 5 mg/min.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Sweet clover poisoning (moulded dicoumarol): Plumb’s p.976 (Oehme 2009): sweet clover or lespedeza toxicity 1–1.5 mg/kg SC for several days; remove the source and avoid stress. WITHDRAWAL — Plumb’s: the labelled injection carries no withdrawal times.
• Anticoagulant rodenticide toxicity: Papich 5e and Plumb’s p.976 (Upson; Veda-K1 label): 0.5–2.5 mg/kg IM or SC. For acute haemorrhage IV only if essential — diluted, no faster than 10 mg/min in adults, 5 mg/min in young animals. Second-generation agents may need 3–4 weeks (Bailey 1986).

Birds

• Raptor / songbird secondary rodenticide poisoning: Papich 5e: birds 2.5–5 mg/kg q24h. Plumb’s p.976: 0.2–2.5 mg/kg IM as needed, usually 1–2 injections (Clubb 1986); 0.25–0.5 mL/kg IM of the 10 mg/mL product before surgery (McDonald 1989).

Rabbits

• Rabbit rodenticide ingestion: Plumb’s p.976: pocket pets are treated at the high end — loading dose 2.5–5 mg/kg PO, then 3–5 mg/kg/day PO divided twice daily (Merola 2002); injectable given PO at 5 mg/kg/day divided q8–12h with a fatty meal (Richardson 2002). SC injection can cause anaphylaxis; never IV. The calculator range (1.5–2.5 mg/kg q12h) corresponds to the 3–5 mg/kg/day maintenance dose.

Small mammals

• Ferret / guinea pig rodenticide: Plumb’s p.976: rabbits, rodents and small mammals — loading 2.5–5 mg/kg PO, then 3–5 mg/kg/day divided twice daily (Merola 2002), or 5 mg/kg/day divided q8–12h (Richardson 2002); feed with a fatty meal. SC injection can cause anaphylaxis. The calculator range (1.5–2.5 mg/kg q12h) corresponds to 3–5 mg/kg/day divided twice daily.

Contraindications

Hypersensitivity (rare anaphylaxis with IV — IV route is strongly discouraged, use SC if parenteral needed). Use with caution in severe hepatic dysfunction (impaired Vit K activation).

Species-specific warnings

Dogs: Second-gen rodenticide protocol: 3–4 weeks of Vit K1 PO with fatty meal. PT check 48–72 h after stopping.

Birds: Secondary poisoning common in raptors / songbirds; rehab protocol 2.5–5 mg/kg IM daily × 3 weeks.

Adverse effects

• Rare anaphylaxis with IV administration (do NOT use IV route)
• Local injection-site reaction (SC / IM)
• PO: rare GI upset

Drug interactions

• Warfarin / anticoagulant rodenticides: Vit K1 IS the antidote
• Antibiotics suppressing gut flora: may reduce Vit K2 production but Vit K1 bypasses this
• Cholestyramine / orlistat: reduce Vit K1 absorption

Pregnancy and lactation

Safe in pregnancy.

Monitoring

• PT (prothrombin time) — baseline, then 48–72 h after stopping Vit K1 to confirm cessation is safe
• Clinical signs: bleeding, dyspnoea (pleural haemorrhage), pallor
• PCV / haemoglobin during active bleeding
• CBC weekly during 2–4 week course
• If PT remains elevated 48–72 h after stopping → CONTINUE Vit K1 another 2 weeks

Toxicity and overdose

Wide safety margin orally. IV anaphylaxis: serious historical concern with Vit K1 IV — never use IV route. SC / PO are safe.

Management: Acute oral overdose: GI upset. Supportive care. No specific antidote needed.

Clinical pearls

• GIVE WITH FATTY MEAL — bioavailability triples with fat in the stomach
• NEVER GIVE IV — anaphylaxis risk is real; use SC if parenteral needed
• Second-generation rodenticide (brodifacoum / bromadiolone — the most common in modern bait): minimum 3 weeks of treatment
• PT at 48–72 h after stopping is the cessation test — if elevated, restart for another 2 weeks
• Actively bleeding patient: SC Vit K1 + fresh-frozen plasma (gives immediate clotting factors) + supportive care
• Owner counselling — they must complete the full 3–4 weeks even when the dog appears fine. Treatment failure → death.
• Raptor / wildlife with secondary exposure: 2.5–5 mg/kg IM daily × 3 weeks is standard wildlife-rehab protocol

Mechanism of action

Vitamin K1 (phylloquinone) is a required cofactor for hepatic gamma-carboxylation of coagulation factors II, VII, IX, X (and proteins C, S). Anticoagulant rodenticides inhibit vitamin K epoxide reductase, preventing recycling of Vit K — so the patient becomes "Vit K deficient" despite adequate dietary intake. Supplemental Vit K1 bypasses the inhibition by providing exogenous reduced Vit K. PO bioavailability is excellent WITH FATTY MEAL.

Formulations and products

• Vitamin K1 capsule 5 mg
• Vitamin K1 capsule 25 mg
• Vitamin K1 capsule 50 mg
• Vitamin K1 injection 10 mg/mL

Storage

Capsules: 15–25 °C dry. Injection: 15–25 °C protected from light. Multidose vial: discard 28 d after broaching.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other hormones, emergency drugs, supplements and other drugs

• Penicillamine (D-Penicillamine)
• Pentoxifylline
• Pergolide
• Phenylpropanolamine (PPA)
• PMSG / eCG (Pregnant Mare Serum Gonadotrophin)
• Potassium Bromide (KBr)
• Pralidoxime (2-PAM)
• Prazosin

Frequently asked questions