EPM Treatment Summary

Once a diagnosis of EPM is established, treatment of the horse should start immediately.  A delay in treatment allows the disease to progress, potentially causing additional permanent damage to the central nervous system.  Treatment is usually with drugs known to kill or retard the reproduction of the protozoa S. neurona.

This web site is based upon information found in veterinary journals and clinical studies.  Drugs or remedies which have not been studied in a clinical trial are not covered here.  The FDA has approved four drugs for the treatment of EPM, some of which are not on the market, and some available as compounded drugs.

© Johny Day  Beard Trimming

All of the medications listed below require a prescription by a licensed veterinarian.  Some veterinarians stock the medications, and will sell them to the owner.  Other veterinarians will issue a prescription for the drug.  The drugs are available on the internet, with a prescription.  The laws concerning who may order the drug, the owner or the veterinarian, vary depending on the state where the pharmacy is located.

The veterinarian may also prescribe the use of an anti-inflammatory, immune stimulant, and/or vitamin E during treatment.  Most veterinarians will suggest that the horse not be ridden or worked for some time, dependant on the severity of symptoms.  Giving the horse time off will help keep its stress to a minimum, and allow the immune system to heal.  Read the page on Other Therapies for items to accompany the treatment drugs.

About EPM Drugs

All of the drugs require a minimum number of days to build the concentration of drug in the cerebrospinal fluid to a level that will kill or impede the protozoa.  It is important that the horse receives the medication every day and generally at the same time of day.  All four listed medications are given orally.

All four drugs fall within the range 57% to 61% success rate, based upon clinical studies.  Two major differences between the drugs are cost and possible side effects.  A successful treatment is deemed one in which the neurological symptoms are reduced by 1 on the Mayhew Scale.  This is not very comforting to an owner with a horse at 4 on the Mayhew Scale.  A successful treatment under this definition may leave the horse safe for pasture only.

There is disagreement between researchers over the effectiveness of longer or stronger drug protocols.  Clinical trials and veterinarian experience suggest that it is often necessary to continue the treatment beyond the FDA labeled length of time.  Additional improvement in neurological symptoms has been shown in trials extending the treatment length.  Some veterinarians may suggest the use of ponazuril or diclazuril at higher than label doses.

Sulfadiazine - Trimethoprim - Pyrimethamine Combination

February 2009 Cost for compounded drug $65-190/month, ReBalance N/A

This drug, in different combinations is one of the first drugs used to treat EPM.  The FDA approval was issued to ReBalance for a sulfadiazine-pyrimethamine combination.  As of February 2009 Rebalance was not on the market, but may return.

This drug acts on S. neurona by limiting folic acid uptake by the protozoa, inhibiting its ability to reproduce.  It does not kill the protozoa, and must be given long enough to limit reproduction until the infection has died out, three to seven months.  This drug also limits folic acid uptake by the horse.  “Because of the greater frequency and severity of bone marrow suppression at the 2X dose level, REBALANCE Antiprotozoal Oral Suspension should be administered at the labeled 1X dose level.”  It should be given according to an accurate animal weight.  Supplementation with folic acid to avoid anemia is controversial.  This drug must be given at least one hour before food.  The horse should be routinely monitored by blood tests for anemia, as 22% of the horses in the clinical study became anemic.

“The combination of pyrimethamine, and sulfa may cause anemia, decreased platelets, decreased white blood cell counts, and suppress bone marrow. Pyrimethamine should be used with extreme caution in animals with blood dyscrasias or bone marrow suppression,” indicates Wedgewood Pharmacy.

In Compendium Equine Jan/Feb 2008, Dr. Robert MacKay suggests using this drug simultaneously with diclazuril or ponazuril to treat relapses.  It is available from many compounding pharmacies including:

 Wickliffe Pharmacy   (888) 934-5678

Wedgewood Pharmacy  888-678-1967

Diclazuril (Protazil)

June 2009 compounded cost $150-$300/28 days, Protazil N/A

Protazil, FDA approved March 2007, is not yet on the market.  Because diclazuril is approved, but not available commercially, it can be obtained through veterinary compounding pharmacies.  This drug is based upon an herbicide, and attacks the chloroplast function of the protozoa.  It is considered non-toxic at higher doses in mammals, and had no reportable side effects in trials.  This drug may be given with or without food, and it is not known if supplemental fat (corn oil) increases absorption.  Protazil was labeled at 1mg/kg body weight, but was shown in a study to have higher relapse rates at that level, than other drugs.  A commonly compounded diclazuril rate is 5.0mg/kg body weight.  In Compendium Equine Jan/2008, Dr. Robert MacKay suggests treating relapses using diclazuril at 7mg/kg body weight.  Available from the following compounding pharmacies:

Axtell Rite Value Pharmacy    903-564-3216

Medicine Shoppe, York, PA    717-846-0500

Ponazuril (Marquis)

February 2009 internet cost for Marquis, $750-$850/28 days, compounded N/A

Ponazuril is in the same class of drugs as diclazuril.  It is not available compounded.  This drug is also based upon an herbicide, and attacks the chloroplast function of the protozoa.  It is considered non-toxic at higher doses in mammals, and has minor side effects including rash and blisters.  This drug may be given with or without food, and immediately giving additional fat (corn oil) will help absorption.  Marquis is labeled at 5mg/kg body weight, and is given once per day.  In Compendium Equine Jan/2008, Dr. Robert MacKay suggests treating relapses using Marquis at 35mg/kg body weight per day for the first four days, then 5mg/kg for 28 days.

Nitazoxanide (Navigator)

February 2009 IDEXX Labs stopped making Navigator, stock no longer available

Navigator generally cost more than Marquis, and according to the package insert, had potentially serious side effects such as enterocolitis, laminitis, anorexia, fever, and lethargy.  It was toxic at levels above the labeled use, and an accurate animal weight was necessary for proper administration.  In two field studies 27% and 31% of horses had adverse reactions while on the drug.  A not-yet-published manuscript indicates that IDEXX is testing a new formulation of NTZ without the nitrogen.

June 2009

References:

Rebalance Freedom of Information Summary Open PDF

Protazil Freedom of Information Summary  Open PDF

Marquis Freedom of Information Summary Open PDF 

Navigator Freedom of Information Summary Open PDF

Navigator package insert:
Insert is no longer available on IDEXX website.
Information is contained in FOI above.

Pyrimethamine
http://www.wedgewoodpharmacy.com/monographs/pyrimethamine.asp

Compounded diclazuril:  https://secure.francks.com/docs/equine_med_list.pdf

“EPM: Managing Relapses”, Compendium Equine Jan/Feb 2008
Click here to open pdf.

AAEP Proceedings, Vol 54, 2008

www.TheHorse.com  articles 8696, 10416

Eq Vet ED, vol 12, #4, June 2000, 195-200.

Clin Tech Equine Pract 5:9-16 2006

Navigator and new compound J Vet Para.2009.03.22

 

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