Understanding Toltrazuril Paste for Horses with EPM: What Horse Owners Should Know

Equine Protozoal Myeloencephalitis (EPM) is one of the most challenging neurological diseases in horses. Caused primarily by the protozoan Sarcocystis neurona, EPM can lead to muscle atrophy, incoordination, and even death if not treated early and aggressively. One treatment that’s gaining more attention in recent years is Toltrazuril paste, an off-label but promising option in the fight against EPM.

What is Toltrazuril?

Toltrazuril is an antiprotozoal agent initially developed for use in livestock and poultry to combat coccidiosis. It works by disrupting the reproduction and energy metabolism of protozoa, effectively stopping their lifecycle. Though not FDA-approved specifically for horses in the U.S., it's been used off-label in veterinary medicine for conditions involving protozoal infections — including EPM.

Why Consider Toltrazuril Paste for EPM?

Most traditional EPM treatments involve FDA-approved drugs like Ponazuril (Marquis) or Diclazuril (Protazil). However, Toltrazuril is considered by some veterinarians as a stronger precursor to Ponazuril, as it has a broader protozoacidal effect and may be more effective in some horses, especially in stubborn or relapsing cases.

Key Benefits:

Broad-spectrum activity against protozoa

Long half-life, allowing sustained therapeutic levels

High efficacy in early studies and anecdotal cases

May cross the blood-brain barrier, targeting the central nervous system — the site of EPM lesions

How is It Used?

Toltrazuril is typically compounded into a paste or suspension form for oral administration. Dosage can vary depending on the severity of the infection and the horse's weight, but a common regimen may range from 10–20 mg/kg once daily for a period of 28 days or more.

Note: Since this is an off-label treatment, it should only be used under veterinary supervision.

Side Effects and Considerations

While generally well tolerated, potential side effects of Toltrazuril may include:

Mild gastrointestinal upset

Changes in liver enzyme levels with prolonged use

Because it's not officially approved for equine use in the U.S., sourcing Toltrazuril paste typically involves working with a compounding pharmacy or through a veterinarian experienced in off-label treatments.

The Bottom Line

Toltrazuril paste isn’t a silver bullet, but for some horses with EPM — particularly those that don’t respond to traditional therapies — it can be a game changer. As with any treatment, early diagnosis, appropriate dosing, and close veterinary monitoring are key to giving your horse the best chance at recovery.

If you suspect your horse has EPM or if you’re exploring alternative treatment options, talk to your vet about whether Toltrazuril paste might be right for your situation.

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