Ponazuril
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: 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 โ Disruption of the organism's ability to synthesize essential fatty acids and amino acids โ **Protozoal death** (cidal activity).
Dosing by species
- Neosporosis or Toxoplasmosis ยท 7.5-15 mg/kg PO once daily ยท PO ยท q24h ยท 28 days ยท Dose extrapolated between doses for horses and mice.
- Coccidiosis ยท 20 mg/kg PO daily ยท PO ยท q24h ยท 3 days ยท Must be compounded for administration in kittens or cats. Associated with rapid resolution of diarrhea.
- Equine Protozoal Myeloencephalitis (EPM) ยท 5 mg/kg PO once daily ยท PO ยท q24h ยท 28 days ยท See package insert for specific dosing instructions.
- Cryptosporidium respiratory disease (Falcons) ยท 20 mg/kg PO once daily ยท PO ยท q24h ยท 7 days ยท Given as a compounded suspension.
- Adjunctive treatment of Eimeria species (Rabbits) ยท 20 mg/kg PO q24h ยท PO ยท q24h ยท 7 days
- Eimeria macusaniensis (Camelids/Crias) ยท 20 mg/kg PO once daily ยท PO ยท q24h ยท 3 days ยท Dilute paste to 100 mg/mL before administration (e.g., 40g paste + distilled water to 60g total).
- Neosporosis or Toxoplasmosis ยท 7.5-15 mg/kg PO once daily ยท PO ยท q24h ยท 28 days ยท Dose extrapolated between doses for horses and mice.
Routes of administration
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)
Monitoring
- Clinical efficacy and resolution of neurological or gastrointestinal signs
- Tear production (Schirmer Tear Test) in dogs, especially predisposed breeds
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).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.