The U.S. Food & Drug Administration announced July 23 that it is 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.
FDA said two horses in Maine and one in Ohio ultimately died or were euthanized as a result of the incident.
According to FDA, toltrazuril is not approved by the agency for use in horses. FDA said it has serious safety concerns about unapproved animal drugs, including certain compounded animal drugs, because they are of unknown quality and have not been evaluated by FDA for safety and effectiveness.
Unapproved animal drugs also may not be labeled appropriately, which could potentially result in unsafe use of the product, FDA said.
Furthermore, FDA said it recently finalized testing that revealed that this lot of product contained approximately 18-21 times the pyrimethamine indicated on the labeling. High doses of pyrimethamine can cause symptoms such as seizures, fever and death in horses.
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). This product lot is accounted for and is no longer in distribution, FDA said.
The firm learned of the adverse events on May 24 and initiated a recall to the consumer/user level the same day. FDA is working with Rapid Equine Solutions and state partners to investigate these adverse events.
According to FDA, a previous incident in 2014 linked to a different compounder also involved erroneously formulated compounded pyrimethamine/toltrazuril products that led to the deaths of four horses.
The agency said it is important to note that compounded products are not FDA-approved animal drugs. FDA said it has approved several drug products for the treatment of EPM, and horse owners should consult their veterinarian for treatment advice.
FDA encourages horse owners, caretakers and veterinarians to report adverse events (such as seizure, fever or collapse) to FDA in horses being treated with compounded pyrimethamine-containing products.
Owners and veterinarians can report complaints about animal drug products by following the instructions at How to Report Animal Drug Side Effects and Product Problems.