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