🩸 Vitamin K₁ Vet Guide 2025 by Dr Duncan Houston

Welcome to this complete veterinary guide on **vitamin K₁ (phytonadione)** usage in horses. In young or adult equines, this essential fat‑soluble vitamin is the **antidote for rodenticide poisoning** and toxic moldy sweet‑clover ingestion. We’ll cover what it does, when to use it, dosing, administration, side effects, monitoring, and practical clinical advice. 🐴✨

🔎 What Is Vitamin K₁ and Why It Matters

Vitamin K₁ (phytonadione) is essential for activating clotting factors II, VII, IX, and X in the liver. Insufficient clotting leads to **severe bleeding**, seen in anticoagulant rodenticide toxicity (like warfarin or brodifacoum) or ingestion of moldy sweet clover containing dicumarol :contentReference[oaicite:2]{index=2}.

Injectable K₁ restores clotting function by reversing these toxic impacts—making it **life-saving** in acute bleeding cases. It can be administered **subcutaneously (SC)** or **intramuscularly (IM)**. Intravenous (IV) is possible but risky and only in emergencies :contentReference[oaicite:3]{index=3}.

⚠️ When to Use Vitamin K₁ in Horses

• Confirm or presumed ingestion of **anticoagulant rodenticides** (rat/mouse poisons).
• Long-term ingestion of **moldy sweet-clover hay**.
• Suspected coagulopathy from **liver disease, malabsorption**, or chronic antibiotics interfering with vitamin K recycling :contentReference[oaicite:4]{index=4}.

💉 Dosing Protocols

Dosing must be adjusted based on **severity and chronicity**.

Acute, Hemorrhagic Cases:

• Give **0.5–2.5 mg/kg** SC or IM. IV only if bleeding is life‑threatening and SC/IM not feasible. Administer slowly—no more than 10 mg/min in adults, 5 mg/min in young :contentReference[oaicite:5]{index=5}.

Non‑Acute or Maintenance Cases:

• 0.5–2.5 mg/kg SC or IM (every 12–24 hours), depending on response :contentReference[oaicite:6]{index=6}.
• Continue until clotting times normalize—typically 1–2 weeks; long-acting rodenticides may require longer :contentReference[oaicite:7]{index=7}.

Administer all injections into the **neck or large muscles**, alternating sites to avoid local reactions.

⚕️ Administration & Safety Tips

• Wear gloves; use sterile syringe.
• Keep injection site clean to reduce reactions.
• Avoid IV unless necessary—can cause serious allergic reactions or anaphylaxis :contentReference[oaicite:8]{index=8}.
• Dilute only with saline or dextrose if needed, and use immediately :contentReference[oaicite:9]{index=9}.

⚠️ Side Effects & Monitoring

• SC/IM injections can cause **mild swelling, pain or hematoma** :contentReference[oaicite:10]{index=10}.
• IV injections carry **anaphylaxis risk**—stop immediately and treat if reactions occur :contentReference[oaicite:11]{index=11}.
• Poor response may indicate ongoing toxin exposure, liver disease, or coagulopathy.

**Baseline labs** (PT, aPTT, CBC, biochemistry) should be taken before initial dose. Recheck clotting time every 6–12 hours initially, then daily until stable :contentReference[oaicite:12]{index=12}.

📅 Treatment Timeline

• Day 0: Administer first dose.
• Within 6–8 hours: Recheck PT/aPTT; readminister if needed.
• Repeat daily injections until clotting normalizes—usually 7–14 days for short-acting toxins, but longer for long-acting rodenticides.
• Taper dose based on labs. After stabilization, switch to oral K₁ if available, and continue until at least 2 weeks post-normalization :contentReference[oaicite:13]{index=13}.

📊 Summary Table

✅ Practical Vet Take‑Home Points

• Don’t wait—start K₁ while confirming diagnosis.
• Laboratory monitoring guides dosing and duration.
• Be cautious with IV route—only use when essential.
• Plan for prolonged therapy with long-acting toxins.
• Educate owners on signs, possible reactions, and hygiene around injections.

📲 Need Support?

For help with dosing calculations, monitoring protocols, or client communication materials, our **Ask A Vet** team is available. Download the Ask A Vet app for 24/7 veterinary guidance on emergency care, hematology interpretation, and dosing charts from your phone! 🌟