Stock photo of horse with EPM.
Four horses are dead after suffering ill effects from a compounded combo drug containing pyrimethamine and toltrazurilused which was used to treat the neurological disorder Equine Protozoal Myeloencephalitis (EPM.)
The U.S. Food and Drug Administration says the product was made by Wickliffe Pharmacy in Lexington, Kentucky. One lot was compounded as a paste and one as an oral suspension. The products associated with these two lots are accounted for and are no longer in distribution.
The FDA began investigating after receiving adverse event reports regarding ten horses — two in Kentucky and eight in Florida. Four have died or were euthanized and six horses are recovering, according to the agency.
FDA testing indicates that one lot contained higher levels of pyrimethamine than the labeling indicates. Adverse events associated with high doses of pyrimethamine include seizures, fever, and death.
The usual dose of pyrimethamine in horses is 1 mg/kg, which has been shown to be safe for the treatment of EPM in an FDA-approved combination product containing pyrimethamine and sulfadiazine.
Compounded drugs are not approved by the FDA. Additionally, toltrazuril is not approved for use in horses.
Drugs that have been evaluated and approved by FDA for the treatment of EPM include ponazuril, diclazuril, and a combination drug of pyrimethamine and sulfadiazine.