💊 Vet’s 2025 Guide to Rifampin for Horses

By Dr Duncan Houston BVSc

1. Introduction & Mechanism

Rifampin is a powerful antibiotic used off‑label in horses, primarily for intracellular or abscess‑forming infections. It works by inhibiting bacterial RNA polymerase, making it effective against tough pathogens like Rhodococcus equi, Corynebacterium pseudotuberculosis, and certain staphylococci :contentReference[oaicite:3]{index=3}.

2. Key Indications

• **Rhodococcus equi pneumonia in foals** — Always used in combination with a macrolide (e.g., erythromycin or clarithromycin) to enhance treatment success :contentReference[oaicite:4]{index=4}.
• **Internal abscesses** from organisms like staph, strep, or **Corynebacterium**, again combined with penicillins or cephalosporins :contentReference[oaicite:5]{index=5}.
• **Potomac horse fever**—used with erythromycin as an oral alternative to oxytetracycline :contentReference[oaicite:6]{index=6}.

3. Dosing & Administration

• **Rhodococcus equi**: 5 mg/kg PO every 12 h alongside a macrolide antibiotic :contentReference[oaicite:7]{index=7}.
• General staph/abscesses: 10 mg/kg PO every 24 h, with concurrent antibiotic therapy :contentReference[oaicite:8]{index=8}.
• Administer on an empty stomach when possible to maximize absorption :contentReference[oaicite:9]{index=9}.

4. Combination Therapy & Resistance Prevention

Using rifampin alone leads to rapid resistance. Always combine with another antibiotic—macrolide for R. equi, penicillin or cephalosporin for other infections :contentReference[oaicite:10]{index=10}. Overuse can drive resistance on farms :contentReference[oaicite:11]{index=11}.

5. Side Effects & Monitoring

• **Gastrointestinal upset**—foals on macrolide combos may develop diarrhea :contentReference[oaicite:12]{index=12}.
• **Liver issues**—monitor enzymes; horses may rarely show hepatic dysfunction :contentReference[oaicite:13]{index=13}.
• **Red-orange body fluids** (urine, tears, sweat)—harmless but may stain gear :contentReference[oaicite:14]{index=14}.

6. Pharmacokinetics & Safety

Rifampin is well absorbed in horses; widely distributed in tissues—including within cells and abscesses—to enhance bacterial reach :contentReference[oaicite:15]{index=15}. Avoid use in animals destined for human consumption—no withdrawal times exist—and it may produce hepatic tumors in lab rodents :contentReference[oaicite:16]{index=16}.

7. Administration Forms

Commercial oral suspension (150–300 mg/mL) is commonly used under prescription :contentReference[oaicite:17]{index=17}. Human rifampin capsules or compounded formulations are used when veterinary versions are unavailable.

8. Drug Interactions & Contraindications

• May speed up metabolism of co-administered drugs—monitor critically!
• Avoid with hepatotoxic drugs; discontinue if jaundice appears.
• Not to be used in breeding stock intended for food animals.

9. Case Study: “Gemini” the Foal

A 6-week-old foal with severe R. equi pneumonia received clarithromycin (7.5 mg/kg q12 h) and rifampin (5 mg/kg q12 h). Respiratory signs improved markedly within 7 days, with resolution by 4 weeks and no diarrhea noted—thanks to gradual GI support.

10. Best-Practice Protocol

11. Ask A Vet Support 🩺

At Ask A Vet, we assist with antibiotic protocols—dose adjustments, monitoring plans, resistance checks, and farming biosecurity. If your horse is on rifampin, message anytime via the app for veterinary support, tailored to your horse's health journey. Download Ask A Vet now for expert guidance in 2025! ❤️

12. Final Take‑Home Points

• Rifampin is a potent intracellular antibiotic used off-label in horses—best in combination therapy.
• Doses: 5 mg/kg q12 h for R. equi, 10 mg/kg q24 h for abscesses.
• Monitor for GI upset and liver effects; red-orange fluid discoloration is expected but harmless.
• Strict use protocols and monitoring help prevent resistance.
• Consult your vet, and rely on Ask A Vet support for dosing, duration, and welfare monitoring.