EPM Drug Available Direct To Veterinarians

The Food and Drug Administration is allowing licensed veterinarians to submit a request to be allowed to import Diclazuril from Canada to treat horses affected by equine protozoal myeloencephalitis (EPM). Diclazuril is licensed for use in Canada in broiler chickens, but the FDA is willing to let veterinarians import a limited amount of the drug for use in no more than four horses.

Veterinarians must notify clients that the drug does not have FDA approval. They also must agree that the drug will not be used in any food animal, and to notify the FDA if there are any adverse reactions.

A statement from the FDA to veterinarians notes: “This document is not intended to endorse the use of Diclazuril in horses for the treatment of equine protozoal myeloencephalitis (EPM). The treatment with the greatest information relative to its efficacy at this time is the use of a dosage of pyrimethamine and an appropriate sulfonamide.

“You should realize that regardless of popular press information, there is little information to support the efficacy of this drug for treatment of equine protozoal myeloencephalitis. In vitro testing indicates that the drug is only coccidiostatic for Neospora caninum at pharmacologic concentrations, while pyrimethamine was coccidiocidal. Pharmacokinetic and bioavailability is in question, or at least not well characterized. At the date noted above (Oct. 20, 1997), there is no confirmed case of EPM that has become negative on CSF antibody testing subsequent to use of diclazuril as recommended. Cases of EPM have become negative after treatment with a sulfonamide and pyrimethamine at appropriate doses. There are rumors that a few horses became negative after the use of Diclazuril, but after five months of treatment at the dose listed below. This information has yet to be confirmed. In addition, Tom Tobin (MVB, MSc, PhD, MRCVS, Diplomate American Board of Toxicology, of the Gluck Equine Research Center), who is evaluating this drug for the treatment of EPM, is concerned over the over-confidence in this treatment.

“A dosage for this drug has not been defined. Some literature citations of uncontrolled studies in non-peer reviewed publications suggest a dosage as indicated below. Other dosages may be inserted.

“The drug comes in a 20 kg bag. It has been suggested that this is sufficient for a 1,000-pound horse. Dose at 250 gm, orally, BID, for 28 days (2.5 gm/1,000 pounds body weight per day). This is not a dosage recommendation. Its purpose is to state a dose cited in common use. This dosage has not been demonstrated to be effective, and other dosages of the drug may be more appropriate.

“It is also possible that this drug is of no benefit whatsoever for this condition at pharmacologic doses.”

Veterinarians who are members of the American Association of Equine Practitioners can obtain a copy of this request to import Diclazuril by using the organization's Fax On Demand service. A table of contents for the Fax On Demand can be obtained through the Members section on the AAEP Web page at www.aaep.org. Non-AAEP members can contact the FDA at 301/594-1692.

Diclazuril is licensed for use in Canada by Pharmacia Upjohn. It was noted by one researcher that this is the first time that he could recall the FDA allowing direct importation by veterinarians of a non-U.S.-licensed drug for use in equines.

Bill Bernard, DVM, Diplomate ACVIM, of the Rood and Riddle Equine Hospital in Lexington, has dealt with numerous cases of EPM. He said he thought it was good that the FDA was taking an interest in this disease, and that it looks like Diclazuril “is probably safe and may be beneficial. At least it is an alternative therapy for EPM. This is not to say it is better (than the conventional therapy), but it is an alternative.”

About the Author

Tim Brockhoff

Tim Brockhoff was Staff Writer of The Horse:Your Guide to Equine Health Care from 1995 to 1999. His degree is in Agricultural Communications from the University of Kentucky, and his equine experience is with American Saddlebreds.

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