The U.S. Food and Drug Administration has linked at least three horse deaths to the use of a compounded drug product containing pyrimethamine and toltrazuril.
Rapid Equine Solutions, LLC of Aston, PA, compounded the product, which was labeled as containing toltrazuril 416 mg/ml and pyrimethamine 17 mg/ml, packaged in 60 ml oral paste syringes for the treatment of the neurologic disease Equine Protozoal Myeloencephalitis (EPM). The product in question, however, contains 18 to 21 times the labeled dose of pyrimethamine, according to FDA tests. Overdoses of pyrimethamine have in the past led to seizures, fever, and death in equines.
FDA notes that compounded products are not FDA-approved animal drugs, and that toltrazuril is not FDA-approved for use in horses.
The FDA encourages veterinarians and horse owners to report adverse events such as seizure, fever, or collapse in horses being treated with compounded drugs containing pyrimethamine. FDA provides a website, “How to Report Animal Drug Side Effects and Product Problems,” to facilitate reporting of adverse drug events.
For more on compounded drugs, see these articles from BovineVetOnline: