In this article
🐴 Vet’s 2025 Guide to Ponazuril (Marquis®) for Horses
By Dr Duncan Houston BVSc
1. Why Ponazuril Matters
Ponazuril (trade name Marquis®) is the current gold standard in treating equine protozoal myeloencephalitis (EPM), offering a powerful, targeted treatment with an excellent safety record. As a vet, I emphasize early intervention with ponazuril to protect neural health and performance longevity. This 2025 guide covers its mechanism, dosing, side effects, monitoring, protocols, and real-world use. 🧠
2. What Is Ponazuril?
Ponazuril—a 15% oral paste—is an antiprotozoal that inhibits protozoal enzyme pathways and DNA synthesis, leading to death of Sarcocystis neurona and Neospora hughesi organisms :contentReference[oaicite:3]{index=3}.
3. How Ponazuril Works
The active ingredient interrupts protozoal pyrimidine formation, preventing DNA replication and killing the parasite. This makes ponazuril a potent equine neuroprotectant when administered properly :contentReference[oaicite:4]{index=4}.
4. Indications & Off‑label Use
• Primary: FDA-approved for EPM in horses caused by Sarcocystis neurona :contentReference[oaicite:5]{index=5}.
• Off‑label: Used by veterinarians in other species for protozoal conditions (coccidia, Neospora, Toxoplasma) :contentReference[oaicite:6]{index=6}.
Always follow vet guidance for off‑label cases.
5. Dosage & Administration
5.1 Standard Regimen
Typical dosage: 5 mg/kg (2.27 mg/lb) once daily, orally via paste, with a loading dose on day one. Standard course: 28 days but may extend to 60–90 days in complex cases :contentReference[oaicite:7]{index=7}.
5.2 Paste Details
The 15% Marquis paste tube (127 g) treats a 1,200 lb horse for seven days at standard dose :contentReference[oaicite:8]{index=8}.
5.3 Extended Protocols
In refractory or neurological cases, treatment may stretch to 60–90 days depending on clinical signs and vet evaluation :contentReference[oaicite:9]{index=9}.
5.4 Missed Doses
If missed, administer as soon as remembered, then resume normal schedule; do not double-dose :contentReference[oaicite:10]{index=10}.
6. Clinical Benefits
• Effective elimination of neurotoxic protozoa.
• Clinical improvement often seen 14–28 days in.
• Proven long-term neural recovery with proper rehabilitation.
7. Safety & Side Effects
Ponazuril is well-tolerated. Mild soft stools may occur. Serious effects (blisters, seizures) are rare—stop treatment if observed :contentReference[oaicite:11]{index=11}.
8. Monitoring During Treatment
- Neurologic exams every 2–4 weeks.
- Monitor GI health and stool quality.
- Periodic bloodwork for liver/kidney function in prolonged treatment.
- Reassess treatment duration based on clinical response.
9. Adjunct Therapies
- NSAIDs or steroids for neuro-inflammation early in treatment :contentReference[oaicite:12]{index=12}.
- Vitamin E for neural antioxidant support :contentReference[oaicite:13]{index=13}.
- Physical therapy: controlled walks, hydrotherapy, balance exercises.
10. Cost Considerations
Expect $1,000–1,500 per 28-day course for Marquis®, variable with compounding. Extended or repeat treatments add to costs :contentReference[oaicite:14]{index=14}.
11. Compounding & Alternative Formulas
Compounded ponazuril paste or liquid may be prescribed for extensive treatment or when horses reject paste :contentReference[oaicite:15]{index=15}. Use trusted pharmacies to ensure efficacy and safety.
12. Comparison with Other EPM Treatments
| Drug | Form | Duration | Cost/month | Pros/Cons |
|---|---|---|---|---|
| Ponazuril (Marquis®) | Paste | 28–90 days | $1,000–1,500 | Gold standard; well tolerated |
| Diclazuril (Protazil®) | Pellet | 28–90 days | $800–1,000 | Similar efficacy; palatable |
| Sulfadiazine/pyrimethamine (ReBalance®) | Liquid | 90–270 days | $250–400 | Cheaper but longer, anemia risk |
13. Case Study: “Echo” Revisited
Recount "Echo" the mare from Section 9 of EPM article—treated with 60-day ponazuril, NSAIDs, vitamin E, and therapy. Neurologic function and coordination restored by 12 weeks; no relapse at 9-month follow-up.
14. Prevention & Farm Biosecurity
- Secure feed warehouses against opossum intrusion.
- Elevate feed bins; discourage wildlife scavenging.
- Remove carcasses, minimize wildlife habitats near stables.
- Annual neurologic exams for performance horses.
15. Ask A Vet Integration 🩺
At Ask A Vet, we assist with dosing plans, neurologic assessments, lab result interpretation, and rehab strategy. If your horse shows neurologic signs, contact us immediately through the app.
16. Quick Start Table
| Stage | Action |
|---|---|
| Confirm diagnosis | Neuro exam + serum/CSF ratio |
| Begin treatment | Ponazuril paste 5 mg/kg daily + loading dose |
| Support | NSAIDs, vit E, wound care |
| Monitor | Neurologic exams, stools, appetite, bloods |
| Extend if needed | Up to 90 days under vet monitoring |
| Re-evaluate | End therapy if resolved; if not, reassess options |
17. Final Thoughts
Ponazuril remains the frontline treatment for EPM—effective, well-supported, and familiar to seasoned vets. Combined with early diagnosis, supportive care, and rehabilitative protocols, many horses make dramatic recoveries. Trust veterinary guidance and Ask A Vet to steer each step with expertise and empathy. 🌟
Download the Ask A Vet app now for personalised neurologic support, dosing reminders, lab reviews, and 24/7 veterinary access during your horse’s recovery journey. ❤️
