FDA issues emergency use authorization for ivermectin solution to prevent screwworm in horses

The FDA has issued an emergency use authorization (EUA) for Ivermectin Liquid for Horses (ivermectin oral solution) to help prevent New World screwworm (NWS) infestations, also known as myiasis, in horses.

The authorization allows the prescription product to be used for short-term prevention when administered within 24 hours of birth or during initial wound care. It is authorized only for horses and is not FDA-approved.¹

Under federal law, an EUA allows the FDA to authorize the emergency use of an unapproved product or an unapproved use of an approved product during certain public health emergencies declared by the US Department of Health and Human Services. To issue an EUA, the agency must determine that available scientific evidence suggests the product may be effective, that its potential benefits outweigh its potential risks, and that no adequate, approved, and available alternative exists. In the case of NWS, HHS determined that the parasite poses a significant potential public health emergency, allowing the FDA to authorize animal drugs intended to treat or prevent the disease.

NWS is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals. Newborn animals with healing umbilical wounds and animals with open wounds are particularly susceptible because adult flies lay their eggs in these areas. Left untreated, infestations can become severe and life-threatening.

The authorization comes as NWS cases continue to rise in the United States. Since the first US detection since the 1960s was confirmed in Zavala County, Texas last month, 39 cases have been identified across multiple species, including cattle, sheep, goats, and dogs.² Federal officials have warned that an outbreak in Texas alone could have billions of dollars in economic consequences for the livestock industry.

The FDA said available evidence indicates Ivermectin Liquid for Horses may be effective for short-term prevention of NWS myiasis in horses when used as authorized and that its expected benefits outweigh its potential risks. The authorization is the agency's 11th EUA issued in response to NWS.

The EUA does not authorize the product to treat existing infestations. If a wound is already infested or if an infestation develops after administration, owners should contact a veterinarian to discuss treatment options, the agency said.

"This authorization provides a short-term prevention option for horses, but owners and veterinarians should be aware of the limitations," Timothy Schell, PhD, director of the FDA's Center for Veterinary Medicine, said in an announcement.¹ "This product's window of prevention lasts no more than 24 hours, so it is important that the product be used alongside other preventive measures such as bandaging, repellents, and other fly-control methods."

Ivermectin Liquid for Horses is a clear, ready-to-use solution that can be administered as an oral drench or through a nasogastric tube. It is available only by prescription from a licensed veterinarian and is sponsored by Alberta Vet Labs Ltd., a Canadian company. The FDA has published a fact sheet on the EUA, along with a letter to horse owners and veterinarians outlining the authorized use of the product and other FDA-authorized drugs to help prevent NWS in horses.

The authorization is based primarily on pharmacokinetic data and studies conducted in cattle, not horses. The agency noted that no clinical studies have evaluated the product's effectiveness against NWS in horses. A single dose within 24 hours of birth for newborn foals or at the time of initial wound care is recommended, and any preventive effect is likely limited to about 24 hours after administration. Because of that narrow window, the FDA said additional measures such as bandaging, repellents, and other fly-control methods will likely be needed to protect wounds throughout the healing process.

The authorization will remain in effect until it is revoked or until the US Department of Health and Human Services terminates the declaration supporting emergency use authorizations for animal drugs used against NWS.

Other FDA-authorized products for NWS

The ivermectin solution expands the list of products available to help prevent or manage NWS infestations.

The FDA has conditionally approved Credelio Quattro-CA1 chewable tablets (lotilaner, moxidectin, praziquantel, pyrantel), Dectomax-CA1 injectable solution (doramectin injection), and Exzolt Cattle-CA1 topical solution (fluralaner).

The agency has also issued EUAs for Credelio chewable tablets (lotilaner), NexGard chewable tablets (afoxolaner), NexGard COMBO (esafoxolaner, eprinomectin, and praziquantel topical solution), Credelio CAT chewable tablets (lotilaner), Nitenpyram Tablets (nitenpyram), Ivomec injectable solution (ivermectin), Dectomax/Dectomax-CA1 (doramectin injection), F10 Antiseptic Wound Spray with Insecticide, F10 Antiseptic Barrier Ointment with Insecticide, and Negasunt Powder.

References

1. FDA Issues Emergency Use Authorization for Drug for Short-Term Prevention of New World Screwworm in Horses. News release. US Food & Drug Administration. July 15, 2025. Accessed July 16, 2026. https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-drug-short-term-prevention-new-world-screwworm-horses
2. Confirmed Detections of New World Screwworm. US Department of Agriculture Animal and Plant Health Inspection Service. Accessed July 16, 2026. https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/current-status/us-confirmed-cases-new-world
3. Fact Sheet for Veterinarians: Emergency Use Authorization of Ivermectin Liquid for Horses (ivermectin oral solution) for New World Screwworm (NWS). US Food & Drug Administration. July 15, 2025. Accessed July 16, 2026. https://www.fda.gov/media/193613/download?attachment