Doxycycline for Horses Vet Guide 2025 – Dr Duncan Houston 🐴💊

By Dr Duncan Houston, BVSc – comprehensive insights on doxycycline use in equine medicine: indications, dosing, safety, and best practices.

Introduction

Doxycycline is a broad-spectrum tetracycline antibiotic valued for treating tick-borne diseases (like Lyme and anaplasmosis), Potomac Horse Fever, Leptospirosis, R. equi pneumonia in foals, joint infections, and other susceptible bacterial conditions 🧬. Though not FDA-approved for horses, it’s commonly used extra-label under veterinary guidance :contentReference[oaicite:3]{index=3}.

📖 Mechanism of Action

It works by inhibiting bacterial protein synthesis via the 30S ribosome, stopping bacterial growth (bacteriostatic) and allowing the immune system to clear infections :contentReference[oaicite:4]{index=4}.

🏥 Indications in Horses

• Lyme disease – 10 mg/kg PO q12h; may require 2–8 week courses :contentReference[oaicite:5]{index=5}
• Anaplasmosis/Ehrlichiosis – same dose for 10–14 days :contentReference[oaicite:6]{index=6}
• Rhodococcus pneumonia in foals (combined therapy)
• Potomac Horse Fever, Leptospirosis, joint or soft tissue infections, select respiratory infections especially in foals :contentReference[oaicite:7]{index=7}
• Pleuropneumonia/joint infections – used in combination therapy

📏 Pharmacokinetics & Dosing Guidelines

Typical dose in horses is 10 mg/kg PO every 12 hours. For pathogens with higher MIC, 20 mg/kg once daily may be used :contentReference[oaicite:8]{index=8}. Avoid IV use—this has been associated with severe cardiovascular toxicity and fatalities :contentReference[oaicite:9]{index=9}.

⚠️ Safety & Side Effects

• Mostly well tolerated; side effects include diarrhea, colitis, decreased appetite :contentReference[oaicite:10]{index=10}.
• Nephrotoxicity reported, especially with prolonged therapy (>7–10 days), dehydration, or when used with other nephrotoxic drugs :contentReference[oaicite:11]{index=11}.
• Ototoxicity possible but rare :contentReference[oaicite:12]{index=12}.
• Contraindicated in pregnant, lactating horses, young foals—tetracyclines affect bone/teeth :contentReference[oaicite:13]{index=13}.
• Avoid oral administration with feeds high in calcium, iron, or antacids—it reduces absorption :contentReference[oaicite:14]{index=14}.

🩺 Best Practices & Monitoring

• Administer on an empty stomach (at least 8 h before feeding, 2 h after) for optimal absorption :contentReference[oaicite:15]{index=15}.
• Ensure horses are well-hydrated; monitor water intake and hydration status.
• Avoid extra NSAIDs or nephrotoxins for long courses; monitor kidney function by bloodwork when used >7–10 days.
• If diarrhea develops, stop the drug and initiate supportive care with fluids and electrolytes :contentReference[oaicite:16]{index=16}.
• Keep records of dose, time, and response; consult veterinarian with any concerns.

📆 Treatment Duration

• Lyme/anaplasmosis: typically 2–4 weeks; extended based on clinical response and antibody titers.
• R. equi pneumonia: variable, often in combination with macrolides.
• Joint/soft tissue infections: 2–6 weeks; may combine with other antimicrobials.

🚫 Drug Interactions & Contraindications

• Avoid co-administration with calcium, iron, antacids, sucralfate, and bismuth – reduce absorption :contentReference[oaicite:17]{index=17}.
• Use caution with chloramphenicol or other antibiotics.
• Not to be used in pregnant or young horses unless benefit > risk.

📘 Administration Forms

• Human-grade capsules/tablets (e.g. Vibramycin) used off-label :contentReference[oaicite:18]{index=18}.
• Compounded oral powders or pastes (apple flavored) improve compliance and dosing accuracy :contentReference[oaicite:19]{index=19}.
• Do not IV in horses due to risk of fatal cardiovascular side effects :contentReference[oaicite:20]{index=20}.

🐎 Case Example

A 500 kg horse with early Lyme disease treated at 10 mg/kg PO q12h (~2.3 g twice daily) tolerated therapy well with no GI upset. After 4 weeks, clinical improvement and reduced serotiter confirmed successful treatment.

📊 Quick Reference Table

📲 Ask A Vet Support & Conclusion

Doxycycline is a valuable antibiotic in equine medicine when used appropriately—on the correct dose, route, and duration, alongside close monitoring. It’s especially useful for tick-borne and intracellular infections. However, attention to side effects, hydration, and drug interactions is vital to ensure safety.

Need detailed dosing protocols, compounding advice, or monitoring plans? Ask A Vet provides personalized treatment guidance, drug reminders, and telehealth support via our app. Download the Ask A Vet App today for confident and safe doxycycline use. 🐎💡