The U.S. Food and Drug Administration (FDA) has asked animal drug companies to voluntarily revise the labels of some livestock and horse dewormers to add information about antiparasitic resistance.
The drugs involved are those used to treat helminths – internal parasites such as tapeworms and roundworms – in cattle, sheep, goats, poultry, swine, and horses.
The FDA’s request is in response to concern that these parasites are becoming increasingly resistant to drugs that were generally effective against them in the past. Antiparasitic resistance, specifically nematode resistance to dewormers, is both a health and welfare issue for grazing livestock, and potentially threatens animal agricultural production.
FDA officials said they made the request after working with veterinary parasitology experts and the animal health community. The requested labeling changes are for approved animal antiparasitics only, and do not pertain to antimicrobial drug products or antimicrobial resistance.
The new labeling information emphasizes these important points:
Any use of a dewormer can result in the development of antiparasitic resistance. Resistance has been reported for most classes of dewormers.
Proper dosing is critical to the safe and effective use of a dewormer. Underdosing may result in ineffective treatment and can increase the risk of antiparasitic resistance.
Livestock producers and animal owners, together with their veterinarian, should monitor herds and flocks to determine the extent of antiparasitic resistance on a particular farm. Fecal examinations and other diagnostic tests should be used to monitor resistance and determine if a dewormer is effective on a farm.
Dewormers should be used as only one part of an overall internal parasite control program. Relying too heavily on dewormers can increase the risk of antiparasitic resistance. The FDA recommends using sustainable non-drug methods as well – such as rotating pastures, avoiding over-grazing, and managing manure.
The FDA is asking drug companies to add information about antiparasitic resistance to both over-the-counter (OTC) and prescription dewormers within the next 12 months. Some approved dewormers for livestock and horses require a prescription, but most are OTC. The FDA said it believes more detailed information about the proper use of OTC dewormers and ways to monitor resistance will help livestock producers and animal owners use these products safely and effectively.
“Antiparasitic resistance is particularly concerning in grazing animals, such as horses, sheep, goats, and cattle. Because these animals are continually exposed to worm eggs on the pasture, they can have repeated parasite infections,” an FDA spokesperson said. “In addition, a growing number of swine and poultry in the U.S. are being pasture-raised. This increases their chances of being repeatedly exposed to worms, which may then become resistant to dewormers.”
The new labeling information does not replace the need to work with a veterinarian to determine appropriate parasite management strategies for individual animals or herds or flocks.
For more information, visit the FDA’s web page on antiparasitic resistance or these additional FDA resources: