# Ponazuril: veterinary dose and monograph

> Ponazuril is a veterinary antiparasitic. A triazine antiprotozoal (the active sulfone metabolite of toltrazuril) — the licensed treatment for equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona (Marquis paste), and used off-label as an effective… Indications include equine protozoal myeloencephalitis (EPM) — Sarcocystis neurona (licensed, Marquis); coccidiosis (Cystoisospora/Eimeria) in dogs, cats, calves, lambs (off-label) — often single/short course; toxoplasma/Neospora-related protozoal disease (adjunct, off-label). This monograph lists 6 reference doses for dogs, cats, horses, rabbits and camelids, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/ponazuril · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Antiparasitic
- **Also known as:** Marquis, Toltrazuril sulfone
- **Species with doses:** Dogs, Cats, Horses, Rabbits and Camelids
- **General dose range:** 5–10 mg/kg PO q24h — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Equine protozoal myeloencephalitis (EPM) — Sarcocystis neurona (licensed, Marquis)
- Coccidiosis (Cystoisospora/Eimeria) in dogs, cats, calves, lambs (off-label) — often single/short course
- Toxoplasma/Neospora-related protozoal disease (adjunct, off-label)

## Ponazuril dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Ponazuril doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Coccidiosis (Cystoisospora) | 50–55 mg/kg | PO | q24h | 3–5 days |
| Neosporosis / toxoplasmosis | 7.5–15 mg/kg | PO | q24h | 28 days |

- Coccidiosis (Cystoisospora): Papich 5e: coccidiosis 50–55 mg/kg once daily PO for 3–5 days. Plumb’s p.988 lists a lower anecdotal regimen — 15–30 mg/kg once, repeated after 7–10 days (Hurley 2007).
- Neosporosis / toxoplasmosis: Plumb’s p.988 (Greene 2006): 7.5–15 mg/kg PO once daily for 28 days — extrapolated from horse and mouse doses.

### Cats

*Ponazuril doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Coccidiosis | 20–50 mg/kg | PO | q24h | 3 days |

- Coccidiosis: Plumb’s p.988 (Marks 2007/2009): 20 mg/kg PO daily for 3 days (compounded). Papich 5e: coccidiosis 50 mg/kg once daily for 3 days; toxoplasmosis 50 mg/kg once or 20 mg/kg daily for 2 days.

### Horses

*Ponazuril doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| EPM (Sarcocystis neurona) | 5 mg/kg | PO | q24h | 28 days |

- EPM (Sarcocystis neurona): Papich 5e and Plumb’s p.988 (Marquis label): 5 mg/kg PO once daily for 28 days; a 15 mg/kg loading dose on day 1 has been used; 50 mL corn oil just before dosing improves absorption and CSF levels.

### Rabbits

*Ponazuril doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Eimeria (adjunct) | 20 mg/kg | PO | q24h | 7 days |

- Eimeria (adjunct): Plumb’s p.988 (Kelleher 2008): rabbits 20 mg/kg PO q24h for 7 days.

### Camelids

*Ponazuril doses for camelids*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Eimeria macusaniensis (crias) | 20 mg/kg | PO | q24h | 3 days |

- Eimeria macusaniensis (crias): Plumb’s p.988 (Walker 2009): 20 mg/kg PO once daily for 3 days; dilute the paste to 100 mg/mL (40 g paste q.s. to 60 g with water).

## Contraindications

Known hypersensitivity. Confirm the diagnosis (EPM in horses; coccidiosis vs other enteritis in small animals). Otherwise few — wide margin. Observe any food-animal considerations for off-label calf use.

## Species-specific warnings

> **Caution:** Horses: For EPM, expect possible transient worsening of signs early in treatment (parasite die-off); confirm the diagnosis and consider anti-inflammatory support.

## Adverse effects

- Generally very well tolerated
- Occasional GI upset / soft stool
- EPM: transient early worsening of neurologic signs possible (parasite die-off)

## Drug interactions

- No clinically important systemic drug interactions reported
- In EPM, sometimes paired with anti-inflammatories to manage early die-off inflammation

## Pregnancy and lactation

Limited data; considered relatively low-risk. Use if clearly indicated.

## Monitoring

- Neurologic response over the 28-day course (EPM)
- Faecal oocyst counts / clinical resolution (coccidiosis)
- Early die-off worsening in EPM (consider anti-inflammatory support)

## Toxicity and overdose

Wide safety margin — overdose is generally well tolerated with at most mild GI signs. The main clinical caution is transient worsening of EPM neurologic signs early in treatment (host inflammatory response to dying parasites).

Management: Supportive; no specific antidote needed given the wide margin. Manage GI upset symptomatically.

## Clinical pearls

- The licensed equine EPM drug (Marquis) — 28 days of daily paste; confirm the diagnosis and watch for transient early neurologic worsening
- Off-label, it is a superb, well-tolerated single-dose COCCIDIOCIDE for pups/kittens/calves (it is the active metabolite of toltrazuril)
- Good CNS penetration is what makes it work for EPM
- Very wide safety margin — one of the better-tolerated antiprotozoals

## Mechanism of action

A triazine that acts on the apicomplexan parasite's apicoplast (a plastid-like organelle) and disrupts development of the intracellular stages of Sarcocystis/coccidia, halting replication. Good blood–brain-barrier penetration allows therapeutic CNS levels for EPM. It is protozoacidal against susceptible stages and well tolerated in mammals.

## Formulations and products

- Oral paste 150 mg/g (15 %, Marquis)
- Compounded oral suspension
- Marquis (Boehringer Ingelheim (Merial)) — 150 mg/g (15 %) oral paste, Oral paste

## Storage

Paste: 15–30 °C, protect from light. Compounded suspension per pharmacy beyond-use date (shake well).

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other antiparasitics

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- [Permethrin](https://vetmasterji.com/drugs/permethrin)
- [Piperazine](https://vetmasterji.com/drugs/piperazine)
- [Praziquantel](https://vetmasterji.com/drugs/praziquantel)
- [Pyrantel pamoate](https://vetmasterji.com/drugs/pyrantel)
- [Pyrimethamine](https://vetmasterji.com/drugs/pyrimethamine)
- [Rafoxanide](https://vetmasterji.com/drugs/rafoxanide)

## Frequently asked questions

### What is the dose of Ponazuril for dogs?

Reference doses for Ponazuril in dogs: 50–55 mg/kg PO q24h for 3–5 days (Coccidiosis (Cystoisospora)); 7.5–15 mg/kg PO q24h for 28 days (Neosporosis / toxoplasmosis). Confirm against the label and the patient before use.

### What is the dose of Ponazuril for cats?

Reference doses for Ponazuril in cats: 20–50 mg/kg PO q24h for 3 days (Coccidiosis). Confirm against the label and the patient before use.

### What is the dose of Ponazuril for horses?

Reference doses for Ponazuril in horses: 5 mg/kg PO q24h for 28 days (EPM (Sarcocystis neurona)). Confirm against the label and the patient before use.

### When should Ponazuril not be used?

Known hypersensitivity. Confirm the diagnosis (EPM in horses; coccidiosis vs other enteritis in small animals). Otherwise few — wide margin. Observe any food-animal considerations for off-label calf use.

### What are the side effects of Ponazuril in animals?

Generally very well tolerated; Occasional GI upset / soft stool; EPM: transient early worsening of neurologic signs possible (parasite die-off).

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.