Two More Horses Dead After Receiving Compounded Medication

The U.S. Food and Drug Administration (FDA) has reported the total number of horses that died after receiving a pyrimethamine/toltrazuril compounded drug from Wickliffe Veterinary Pharmacy, in Lexington, Kentucky, has grown to four, and six others have become ill. 

The FDA said initial testing on one lot of the compounded medication indicates the drug contained higher levels of pyrimethamine than the labeling states. Adverse events associated with high doses of pyrimethamine include seizures, fever, and death, the FDA said in a release issued late May 15. Additionally, the FDA noted, toltrazuril is not currently approved for use in horses.

Earlier this week Robert MacKay, BVSc, PhD, Dipl. ACVIM, professor of Large Animal Medicine at the University of Florida College of Veterinary Medicine, said two Thoroughbreds at a training stable in Ocala, Florida, had died and six others had developed neurologic disturbances within 36 hours of receiving the compound.

The FDA said it has received those eight reports as well as two reports from Kentucky of horses that had suffered adverse effects after receiving the compound.

The compounds in question were in two different lots: one a paste and one an oral suspension. The FDA reported that all of the products in these lots are accounted for and are no longer in distribution.

The compounded drug is used to treat or prevent equine protozoal myeloencephalitis (EPM); MacKay said he was unsure if the treated horses had EPM or if the compound was being used as a preventative.

In a statement, Wickliffe noted that the compound had been prescribed: "The medication prepared by Wickliffe Veterinary Pharmacy was specifically made for and dispensed to the horses for which the medication was prescribed. No other animal patients received the prescribed medication in question."

Because all of the preparations are secured, “any risk of further adverse effects has been eliminated,” the statement continued. “There is no indication that any other products prepared by the pharmacy are unsafe in any way."

Earlier this week Wickliffe released a statement saying it had no indication that the preparation compounded at its pharmacy was unsafe and that it had been prepared as prescribed. On Friday the company said in a release it is working cooperatively with federal health officials on the investigation “to learn more about the cause of the adverse events involving horses that received a compounded product from the pharmacy. 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 FDA is continuing to work with the pharmacy and state regulators to investigate the adverse events.

"During the course of this on-going 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," the FDA said in a release. "The usual dose of pyrimethamine in horses is 1 mg/kg (milligram per kilogram of body weight), which has been shown to be safe for the treatment of EPM in an FDA-approved combination product containing pyrimethamine and sulfadiazine.

"In general, FDA has serious concerns about unapproved animal drugs, including certain compounded animal drugs," the FDA said in its statement. "These drugs are not evaluated by FDA and may not meet FDA's strict standards for safety and effectiveness. Unapproved animal drugs also may not be labeled or advertised appropriately. Horse owners or caretakers should consult with their veterinarians about other therapies."

The FDA said drugs that have been evaluated and approved by the organization for EPM treatment include ponazuril, diclazuril, and a pyrimethamine/sulfadiazine combination.

Originally published on

About the Author

Frank Angst

Frank Angst is a staff writer for The Blood-Horse magazine. An American Horse Publications three-time winner in best news story category, Angst has covered horse racing for more than a decade. Angst spent ten years at Thoroughbred Times, where he earned awards as that magazine’s senior writer and helped launch Thoroughbred Times TODAY. Besides covering horse racing, Angst enjoys handicapping. Angst has written about sports for more than 20 years, including several seasons covering a nationally ranked Marshall Thundering Herd football team.

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