December 6, 2018
The U.S. Food and Drug Administration has requested that animal drug companies voluntarily revise the labels of their approved anthelmintics for livestock (cattle, sheep, goats, poultry and swine) and horses to add information about antiparasitic resistance. The new labeling information is intended to help end-users, including veterinarians, livestock producers, and animal owners, better understand the proper use of anthelmintics and ways to monitor and slow down the development of antiparasitic resistance at the farm level.
Over the coming year, you should begin seeing this new information included on the labels of currently marketed FDA-approved anthelmintics for livestock and horses, as well as on the label of any new anthelmintic that FDA approves for use in these animals.
Antiparasitic Resistance—An Emerging Animal Health Problem
Antiparasitic resistance, specifically nematode resistance to anthelmintics in cattle, small ruminants, and horses, is both a health and welfare issue for U.S. grazing livestock and potentially threatens animal agricultural production. In the U.S., many veterinarians and livestock producers acknowledge that antiparasitic resistance is a severe problem in small ruminants and a growing problem in horses. However, awareness of antiparasitic resistance in cattle is relatively low, even while reports of antiparasitic resistance in this species are increasing. While FDA reviews drugs, including antiparasitic drugs for animals, to determine whether they are safe and effective as part of the approval process, resistance to antiparasitic drugs such as anthelmintics can evolve naturally over time. How veterinarians, producers, and animal owners use these products after approval also affects the development of resistance and the drugs’ continued effectiveness.
By relying solely on antiparasitic drugs for parasite control and using other non-sustainable management practices, such as treating entire herds and flocks based on set protocol instead of actual need, widespread resistance to all major families of broad-spectrum anthelmintics may develop in the near future. To help combat antiparasitic resistance, FDA has developed new labeling information for anthelmintics used in livestock and horses to raise awareness about resistance and increase end-users’ knowledge about appropriate use of these drugs in order to slow down the development of resistance.
The labeling information is not intended to replace the management recommendations that you develop with a specific animal producer or owner, or to direct your practice of veterinary medicine. Rather, the information focuses on how to properly incorporate anthelmintics into an overall internal parasite control program and how to slow down the development of antiparasitic resistance.
New Labeling Information about Antiparasitic Resistance
Cattle, Small Ruminants, and Horses
Antiparasitic resistance is particularly concerning in grazing species (cattle, sheep, goats, and horses). Because these animals are continually exposed to worm eggs on the pasture, they can have repeated parasite infections. FDA has requested that animal drug companies add the following statements to the labels of all anthelmintics for cattle, small ruminants, and horses:
- Parasite resistance may develop to any dewormer, and has been reported for most classes of dewormers.
- Do not underdose. Ensure each animal receives a complete dose based on a current body weight. Underdosing may result in ineffective treatment, and encourage the development of parasite resistance.
- Treatment with a dewormer used in conjunction with parasite management practices appropriate to the geographic area and the animal(s) to be treated may slow the development of parasite resistance.
- Fecal examination or other diagnostic tests and parasite management history should be used to determine if the product is appropriate for the herd/flock, prior to the use of any dewormer. Following the use of any dewormer, effectiveness of treatment should be monitored (for example, with the use of a fecal egg count reduction test or another appropriate method).
- A decrease in a drug’s effectiveness over time as calculated by fecal egg count reduction tests may indicate the development of resistance to the dewormer administered. Your parasite management plan should be adjusted accordingly based on regular monitoring.
Swine and Poultry
Although most swine and poultry in the U.S. are raised in confinement, a growing number of these animals are being pasture-raised. This increases their chances of repeated exposure to parasites which may then become resistant to anthelmintics. FDA is aware that management practices and production schemes for poultry and swine are different than those for grazing species. The agency also understands that the challenges related to parasite biology and diagnostics for poultry and swine differ from grazing species. The labeling statements developed for anthelmintics intended for use in poultry and swine reflect these differences:
Parasite resistance may develop to any dewormer. All dewormers require accurate dosing for best results. Following the use of any dewormer, effectiveness of treatment should be monitored. A decrease of effectiveness over time may indicate the development of resistance to the dewormer administered. The parasite management plan should be adjusted accordingly based on regular monitoring.
Extended-Release Macrocyclic Lactones
FDA has also requested that the labels for anthelmintics that are extended-release macrocyclic lactones include the following additional statement:
Other Warnings: Macrocyclic lactones provide prolonged drug exposure that may increase selection pressure for resistant parasites. This effect may be more pronounced in extended-release formulations.
Over-the-Counter and Prescription Anthelmintics
FDA has requested that animal drug companies add information about antiparasitic resistance to both over-the-counter (OTC) and prescription anthelmintics. Some approved anthelmintics for livestock and horses are prescription only, but most are OTC. For a drug to be approved as OTC, the label must have adequate directions for use that are written in such a way that a non-veterinarian can use the drug safely and effectively. Including information about resistance on the label of OTC anthelmintics is important for communicating adequate directions for use to non-veterinarians. More detailed information about the proper use of OTC anthelmintics and ways to monitor resistance will help livestock producers and animal owners, when working with their veterinarians, use these products safely and effectively.
For more information about the new labeling information and antiparasitic resistance in livestock and horses in general, please see:
- Antiparasitic Resistance
- CVM Update - FDA Working with Stakeholders to Maintain Effectiveness of Livestock and Horse Dewormers
FDA’s Center for Veterinary Medicine (CVM) is committed to promoting and protecting animal health by ensuring safe and effective drugs are available for animals. For more information, please contact CVM’s Education & Outreach Staff at 240-402-7002 or AskCVM@fda.hhs.gov.
FDA’s Center for Veterinary Medicine