Compounded drug may have killed four horses, FDA reports


10 horses in Kentucky and Florida affected by EPM treatment; agency is investigating.

Two lots of products compounded by Wickliffe Pharmacy of Lexington, Ky., have been associated with adverse events in 10 horses, including four deaths, the U.S. Food and Drug Administration (FDA) reports.

Seizures, fever and other clinical signs have been reported in two horses in Kentucky and eight horses in Florida that were administered compounded combination drug products containing pyrimethamine and toltrazuril, used to treat equine protozoal myeloencephalitis (EPM). Four horses have died or been euthanized and six horses are recovering.

The FDA is investigating the products, one compounded as a paste and the other an oral suspension. 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.

“During the course of this ongoing investigation into the adverse reactions, it has come to the attention of FDA that elevated doses of pyrimethamine may have been used by some practitioners with negative results,” a release from the FDA states. “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.”

Wickliffe Veterinary Pharmacy issued a statement May 16 stating the medication was specifically made for and dispensed to the horses for which the medication was prescribed. The pharmacy says it adheres to the highest safety and quality standards of the compounding pharmacy profession and is cooperating with federal health officials in the investigation. “We wish to extend our deepest sympathies to the owners of, and equine professionals associated with, the horses that have died or been euthanized,” the statement reads.

The FDA says the compounded products involved in the investigation were not made from approved animal drugs. Additionally, the FDA says, toltrazuril is not approved for use in horses at all. The FDA is encouraging veterinarians, horse owners and caretakers to report any symptoms such as seizure, fever or collapse in horses who might have received high doses of pyrimethamine.

“The FDA has serious concerns about unapproved animal drugs, including certain compounded animal drugs,” the release states. “These drugs are not evaluated by FDA and may not meet FDA’s strict standards for safety and effectiveness.”

Drugs that have been evaluated and approved by FDA for the treatment of EPM include ponazuril, diclazuril and a combination of pyrimethamine and sulfadiazine. All lots of the compounded products in question have been accounted for and are no longer in distribution.

Veterinarians and horse owners can report complaints about FDA-regulated animal drug products by calling the consumer complaint coordinator in their area or by filing a Veterinary Adverse Drug Reaction report. Information on reporting consumer complaints can be found at

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