The FDA has requested that animal drug companies voluntarily revise the labels of horse dewormers to add information about antiparasitic resistance. | Photo: iStock

The U.S. Food and Drug Administration (FDA) announced Dec. 6 that it has requested that animal drug companies voluntarily revise the labels of drugs intended to treat certain internal parasites in horses and livestock to add information about antiparasitic resistance.

This move comes as a result of the agency’s work with veterinary parasitology experts and the animal health community to find ways to maintain these drugs’ effectiveness. The requested labeling changes are for approved antiparasitic animal drug products only and do not relate to antimicrobial drug products or antimicrobial resistance.

The requested labeling changes specifically affect anthelmintics for horses and livestock (cattle, sheep, goats, poultry, and swine). Anthelmintics, often called dewormers, are animal drugs that treat helminths—several groups of internal parasites, often called worms, that have some similarities, such as tapeworms and roundworms. Helminths are becoming increasingly resistant to drugs that were generally effective against them in the past. In these situations, after an animal is treated with a dewormer, the susceptible worms die and the resistant worms survive to pass on resistance genes to their offspring