FDA Grants First Emergency Use Authorization for Lotilaner to Treat New World Screwworm in Dogs
Key Insights
The FDA has issued the first-ever Emergency Use Authorization for lotilaner (Credelio) to treat New World screwworm (search) infestations in dogs, marking a historic regulatory milestone for animal health.
The authorization is based on a study showing 100% efficacy against screwworm larvae within 24 hours in 11 naturally infested dogs, though data limitations exist regarding U.S. population applicability.
The proactive authorization comes as New World screwworm (search) cases have been confirmed less than 70 miles south of the U.S.-Mexico border, providing veterinarians with a ready treatment option.
The U.S. Food and Drug Administration has granted the first-ever Emergency Use Authorization (EUA) for lotilaner (Credelio, Elanco Animal Health (search)) to treat New World screwworm (search) (NWS) infestations in dogs. This unprecedented regulatory action comes as confirmed cases of the parasite have been detected less than 70 miles south of the U.S.-Mexico border, providing veterinarians and pet owners with a proactive treatment option should the fly enter the United States.
Historic Regulatory Milestone
The EUA represents a significant first for the FDA, marking both the agency's initial emergency authorization for NWS treatment in canines and the first such authorization for any animal drug. The decision reinforces the agency's commitment to providing treatment options in advance of the fly being detected domestically.
"This first-ever Emergency Use Authorization for NWS in dogs gives veterinarians and pet owners peace of mind, knowing there's an authorized treatment option available as soon as they may need it," said Dr. Ellen de Brabander, Executive Vice President of Innovation and Regulatory Affairs at Elanco.
Clinical Evidence and Efficacy Data
The FDA's authorization was based on a peer-reviewed study published in Parasites & Vectors that evaluated lotilaner's efficacy against NWS in naturally infested dogs. The research demonstrated that oral administration of lotilaner at the minimum recommended dosage achieved 100% efficacy against Cochliomyia hominivorax (search) larvae within 24 hours of treatment across 11 naturally infested dogs in Brazil.
The study revealed a rapid onset of action, with larval expulsion rates of 80.5% at 2 hours post-treatment and 93% at 6 hours post-treatment, reaching complete efficacy at 24 hours. Researchers identified the primary mechanism of action as live larval expulsion.
"Lotilaner demonstrated a rapid onset of action and a high efficacy against C hominivorax. We therefore recommend lotilaner for the effective treatment of myiasis (search) in dogs," the study authors concluded.
Data Limitations and Considerations
The FDA and Elanco acknowledge significant limitations in the supporting data. The study was conducted in a limited population of eleven naturally infested dogs in Brazil, and the inferential value to the United States population remains unknown. Additionally, the use of mechanical removal coupled with the lack of a control group confound the ability to define a pure treatment effect.
These limitations highlight the emergency nature of the authorization and the need for additional research to fully establish the drug's effectiveness in U.S. populations.
Understanding New World Screwworm Threat
New World screwworm (search) infestations begin when female NWS flies lay eggs on open wounds or other body parts of live, warm-blooded animals. According to the Centers for Disease Control, wounds as small as a tick bite may attract a female fly to feed and lay her eggs. One female can lay 200-300 eggs at a time and may lay up to 1,000 eggs during her 10- to 30-day lifespan.
Unlike most fly species whose larvae feed on dead and decaying tissue, NWS larvae burrow into the flesh of living animals, causing severe tissue damage and even death if left untreated. This aggressive and invasive nature makes any break in the skin—from a scratch to a surgical incision—a potential entry point for NWS.
Prevention Through Parasite Control
Even before NWS enters the United States, veterinarians and pet owners can take precautions to prevent wounds that create ideal conditions for NWS infection. The U.S. Animal Plant Health and Inspection Service (APHIS) recommends protecting pets and livestock from other wound-causing parasites such as flies and ticks as one way to prevent NWS infestations.
"Preventing or rapidly treating existing wounds is critical to protecting pets from NWS," said Dr. Casey Locklear, a Texas-based veterinarian and parasiticide lead at Elanco. "One way to limit self-inflicted scratching includes using year-round flea and tick protection, such as Credelio."
Authorization Parameters and Safety
The Emergency Use Authorization for lotilaner is authorized only for the duration of the declaration that circumstances exist justifying the emergency use under federal law, unless terminated or revoked sooner. While Credelio is approved for flea and tick treatment, it is not approved for NWS treatment under normal circumstances.
Lotilaner belongs to the isoxazoline class of drugs, which has been associated with neurologic adverse reactions including tremors, incoordination, and seizures. The FDA recommends using caution in dogs with a history of seizures or neurologic disorders. The most frequently reported adverse reactions include weight loss, elevated blood urea nitrogen, increased urination, and diarrhea.