Ponazuril
Toltrazolone sulfone
Also known as: Marquis · Toltrazolone sulfone · ICI-128436 · Ponalrestat
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Neosporosis or Toxoplasmosis | 7.5-15 mg/kg PO once daily | PO | q24h | 28 days | 🌎 NA |
| Coccidiosis | 15-30 mg/kg PO once or repeated after 7-10 days | PO | once or repeated after 7-10 days | 1-2 doses | 🌎 NA |
- Neosporosis or Toxoplasmosis: Dose extrapolated between doses for horses and mice.
- Coccidiosis: Anecdotal
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Neosporosis or Toxoplasmosis | 7.5-15 mg/kg PO once daily | PO | q24h | 28 days | 🌎 NA |
| Coccidiosis | 20 mg/kg PO daily | PO | q24h | 3 days | 🌎 NA |
- Neosporosis or Toxoplasmosis: Dose extrapolated between doses for horses and mice.
- Coccidiosis: Must be compounded for administration in kittens or cats. Associated with rapid resolution of diarrhea.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive treatment of Eimeria species (Rabbits) | 20 mg/kg PO q24h | PO | q24h | 7 days | 🌎 NA |
| Eimeria macusaniensis (Camelids/Crias) | 20 mg/kg PO once daily | PO | q24h | 3 days | 🌎 NA |
- Eimeria macusaniensis (Camelids/Crias): Dilute paste to 100 mg/mL before administration (e.g., 40g paste + distilled water to 60g total).
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Cryptosporidium respiratory disease (Falcons) | 20 mg/kg PO once daily | PO | q24h | 7 days | 🌎 NA |
- Cryptosporidium respiratory disease (Falcons): Given as a compounded suspension.
Reptiles
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Coccidians (Bearded dragons) | 30 mg/kg PO twice 48 hours apart | PO | q48h | 2 doses | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Equine Protozoal Myeloencephalitis (EPM) | 5 mg/kg PO once daily | PO | q24h | 28 days | 🌎 NA |
- Equine Protozoal Myeloencephalitis (EPM): See package insert for specific dosing instructions.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ponazuril is an FDA-approved triazine antiprotozoal primarily indicated for the treatment of Equine Protozoal Myeloencephalitis (EPM) caused by Sarcocystis neurona.
Clinical Pearls:
- Ponazuril is an active metabolite of toltrazuril.
- While officially labeled for horses, it is increasingly used off-label in small animals, exotics, and ruminants for treating coccidiosis, neosporosis, and toxoplasmosis due to its high efficacy and relatively safe profile.
- It crosses the blood-brain barrier, making it effective for central nervous system protozoal infections.
Mechanism of action
Ponazuril targets the apicoplast (plastid body), an essential organelle found specifically in members of the Apicomplexa phylum (which includes Sarcocystis, Toxoplasma, Neospora, and Eimeria).
Inhibition of the apicoplast → Disruption of the organism's ability to synthesize essential fatty acids and amino acids → Protozoal death (cidal activity).
Safety & warnings
Contraindications
- No absolute contraindications noted, but other causes of ataxia should be ruled out before treating for EPM.
Adverse effects
- Blisters on nose and mouth
- Rash or hives
- Diarrhea or loose feces
- Mild colic
- Seizures (rare)
- Keratoconjunctivitis sicca (KCS) in dogs (especially predisposed breeds or at high doses)
Precautions
Safety during pregnancy or in lactating mares has not been evaluated. Use with caution in dogs predisposed to Keratoconjunctivitis sicca (KCS) and monitor tear production. The commercial equine paste is highly concentrated and must be properly diluted/compounded for accurate dosing in small animals and exotics.
Monitoring
- Clinical efficacy and resolution of neurological or gastrointestinal signs
- Tear production (Schirmer Tear Test) in dogs, especially predisposed breeds
Pharmacokinetics
Half-life
Absorption
In horses, approximate bioavailability is 30% when administered orally in water. Bioavailability is significantly enhanced if dissolved in DMSO. In cattle, oral doses are relatively well absorbed.
Distribution
In horses, peak serum levels are reached in about 18 days and peak CSF levels in about 15 days. Peak CSF levels are approximately 1/20th (0.21 mcg/mL) of those found in the serum.
Metabolism
Ponazuril is an active metabolite (sulfone derivative) of toltrazuril.
Elimination
Elimination half-life from serum in horses averages about 4.5 days (108 hours).
Overdose
In horses, daily doses of up to 30 mg/kg (6X the normal dose) primarily caused loose feces. Moderate edema of the uterine epithelium was noted on histopathology for female horses receiving the 6X dose. In dogs, overdose quantities have been associated with the development of Keratoconjunctivitis sicca (KCS).
Available products
Formulations
- Oral paste (15% w/w)
Veterinary
- Ponazuril Oral Paste (15% w/w): 127-gram tubes; each gram contains 150 mg of ponazuril (Marquis)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store the paste at room temperature (15-30°C).
Client information
Important: For this drug to be effective, it must be given exactly as prescribed for the full duration of treatment.
- Adverse Effects: Contact your veterinarian if your animal develops rashes, hives, blisters around the nose/mouth, or gastrointestinal signs (such as diarrhea).
- For Horses with EPM: Clients should be forewarned of the considerable expense associated with this drug. Additionally, clinical improvement may be marginal or not occur at all in some horses, depending on the extent of pre-existing neurological damage.
- For Dogs: Watch for signs of "dry eye" (squinting, redness, or thick mucoid eye discharge) and report them to your veterinarian.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.