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