The U.S. Food and Drug Administration issued a statement July 23, 2019, alerting horse owners and veterinarians that one lot of a compounded combination drug product containing pyrimethamine and toltrazuril has been associated with adverse events in at least three horses. Two horses in Maine and one in Ohio ultimately died or were euthanized as a result.

The FDA recently finalized testing that revealed that this lot of product contained approximately 18 to 21 times the pyrimethamine indicated on the labeling. High doses of pyrimethamine can cause clinical signs such as seizures, fever, and death.

Rapid Equine Solutions LLC, of Aston, Pennsylvania, compounded the product, which was labeled as containing toltrazuril 416 mg/ml and pyrimethamine 17 mg/ml and packaged in 60-ml oral paste syringes for the treatment of the neurologic disease equine protozoal myeloencephalitis (EPM). This product lot is accounted for and is no longer in distribution. The firm learned of the adverse events on May 24, 2019, and initiated a recall to the consumer/user level the same day.

The FDA is working with Rapid Equine Solutions and state partners to investigate these adverse events