The Food and Drug Administration is reminding horse owners and veterinarians of the potential dangers of compounded drugs. The agency issued an advisory on this topic after two lots of compounded combination drug products containing pyrimethamine and toltrazuril, which are used to treat equine protozoal myeloencephalitis, were associated with adverse events in 10 horses in early May.
The products were compounded by Wickliffe Pharmacy of Lexington, Kentucky. One lot was compounded as a paste and one as an oral suspension. All the products in these lots have been accounted for and are no longer in distribution, according to the FDA.
Agency testing has determined that one lot of product contained higher concentrations of pyrimethamine than the labeling indicated. Adverse events associated with high doses of pyrimethamine include seizures, fever, and death.
The FDA received reports of adverse events—including seizures, fever, and death—involving two horses in Kentucky and eight horses in Florida that were administered these products. Four horses had died or been euthanized, and six horses were recovering as of late May.
During the course of its investigation into the adverse reactions, the FDA became aware that high dosages of pyrimethamine may have been used by some practitioners with negative results. The usual dosage of pyrimethamine in horses is 1 mg/kg/d, which has been shown to be safe for the treatment of EPM in an FDA-approved combination product containing pyrimethamine and sulfadiazine. Other drugs that have been evaluated and approved by FDA for the treatment of EPM are ponazuril and diclazuril.
The FDA’s advisory notice said that compounded combination products are not approved animal drugs. Additionally, toltrazuril is not approved for use in horses.
“In general, the FDA has serious concerns about unapproved animal drugs, including certain compounded animal drugs. 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,” according to the advisory notice.
The FDA encourages horse owners and veterinarians to report to the agency any signs such as seizure, fever, or collapse in horses that might have received high dosages of pyrimethamine. Owners and veterinarians can report complaints about FDA-regulated animal drug products by calling the consumer complaint coordinator in their area or by filing a veterinary adverse drug reaction report. Information on reporting consumer complaints can be found here.
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