Four Horses Dead, One Ill; Owner Questions Dewormer

Four horses outside of Hebbronville, Texas, died after they showed clinical signs of an unknown illness in February; one horse is recovering. The horses' owner suspects the animals' problems might have been caused by a dewormer, and she is awaiting necropsy and other test results. The company that manufactured the dewormer found nothing unusual about the product lot in question, and it has notified the Food and Drug Administration (FDA) of the owner's complaint.

On the morning of Feb. 16, the horses' owner, Kerry (who asked that her last name be withheld), noticed five of her horses were acting lethargic, developing fevers, and in some cases were drooling. She immediately contacted her veterinarian.

"They couldn't eat or drink, though they would try to," Kerry said. The horse's symptoms progressed over the next 24 hours to include head pressing, staggering, muscle trembling, sweating, disorientation (they were bumping into things), and finally lateral recumbency (they were unable to rise).

"They would then go down and paddle their feet, and their eyes were glassy looking," she said. "Once they went down like that, they couldn't get up. They were like that until they died." Four days after the first clinical signs, four horses had died, but the fifth showed signs of improvement.

Kerry worried that her other horses might be in danger as well, so she began investigating her farm for the source of the horses' illness.

"We tested everything," Kerry said. "We tested the grain, the water, the weeds in the field; if there's a test for it, we tested it. They've all come back normal." The necropsy results had not been released as of March 6.

"The only difference in the horses that are alive and the ones that are dead is the dewormer," Kerry said. The day before the five horses became ill, Kerry said she dewormed them with a generic brand of ivermectin (Bimectin). She notified Bimeda (, the dewormer's manufacturer, of her suspicion.

Bimeda tested samples from the lot Kerry had used and released a statement that said, "Upon receipt of a Technical Services review from the field, (Bimeda) immediately conducted potency testing on retention samples of Lot 5J019 (the lot in question), and the results were found to be normal and within the original lot release potency specifications pursuant to the product's label claim for active ingredient contents."
Vashti Klein, MA, MBA, a management analyst for the FDA, said, "We have been in contact with the company and encourage the owner to report directly to the company. Veterinarians and animal lovers are encouraged to report adverse experiences for FDA-approved animal drugs. Pre-testing by the manufacturer and review of the data by the government does not guarantee absolute safety and effectiveness due to the inherent limitation imposed by testing the product on a limited population of animals."

According to the company, approximately 58,000 doses from the lot in question have been distributed throughout the United States, with no other reports of safety or efficacy issues. However, the company is offering to replace any products from Lot 5J019 with those from another lot.

Two retailers which offered Bimectin dewormer--Country Supply and Jeffers--temporarily suspended sales of the product until Bimeda could test the product. Country Supply posted a statement on its web site that said, "There is currently a possible safety issue regarding the use of Bimectin." Both companies resumed sales of the dewormer after Bimeda released its test results, with the exception of the lot in question.

Until tests can identify the source of the horses' illness, Kerry said she's worried about her other horses. "I am paranoid; if one of them lies down, I go running outside and start taking their temperatures," Kerry said. "I'm having nightmares about it."

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for .

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