Drugs and medications image
Drugs and medications image EquiMed


PON-az-uh-ril - Pronunciation guide

Brand Names

  • Marquis (15% w/w Ponazuril) Antiprotozoal Oral Paste


Rx symbolPonazuril was the first FDA approved treatment for equine protozoal myeloencephalitis. It works by killing protozoal parasites, including Sarcocystis neurona, which is responsible for causing equine protozoal myeloencephalitis.


Ponazuril is an effective treatment for equine protozoal myeloencephalitis because it crosses the blood/brain barrier, enabling the drug to reach effective levels in the central nervous system and kill the migrating parasite responsible for the disease in the spinal cord.

Dosage and Administration

Prescription medicationPonazuril
Method Dosage
(click row for calculator)
Concentration Period Duration
Oral (paste) 5 mg/kg 150 mg/g 1 Daily 28 days


  • 1Calibrated syringe. Follow veterinary instructions for usage.
  • Federal law restricts this drug to use by or on the order of a licensed veterinarian.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your equine appears to feel better, the entire treatment plan should be completed to prevent relapse.
  • This medication may be available in forms and concentrations not noted in the above table. Always check the label and literature provided with the medication about the form and concentration and DO NOT USE the calculator if the information differs.
  • Calculator is for educational purposes only. Follow your veterinarian's instructions regarding use of this, or any medication.
Method Amount Dosage Period Duration Note
Oral 2.27 mg/lb Daily 28 days

Dose Form: Multidose paste syringes; Each syringe contains enough drug to treat a 1,200 lb horse for seven days

Side Effects

Mild side effects include loose manure, occasional loss of appetite, weight loss, mild colic, blisters of the mouth and nose, skin rash, and hives.


The manufacturer notes that although ponazuril will "effectively clear the horse of S. neurona, it may have no effect on irreparable, pre-existing central nervous system damage caused by the protozoal parasite prior to treatment.".

Relapse is sometimes a problem for horses after treatment and veterinarians are not in agreement about how best to treat these horses.

Many veterinarians increase the recommended length of treatment from 28 days to double that length of time, or 56 days.

Ponazuril is an FDA approved drug for use in horses and is a prescription drug. U. S. federal law restricts this drug to use by or on the lawful written or oral order of a licensed veterinarian.

Ponazuril would be prohibited in any drug-free competition. It is important to check with the individual regulatory group.


Drug literature gives no information about drug interactions with this medication.


No specific information is available about overdose in horses.


Marquis Oral PasteMarquis Oral Paste


About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.