FDA grants emergency use authorization for lotilaner to treat New World screwworm in dogs

The FDA has issued an emergency use authorization for lotilaner (Credelio; Elanco Animal Health) to treat New World screwworm (NWS) infestations in dogs,1 marking the first time the FDA has granted such an authorization for both a NWS treatment in canines and any animal drug. The announcement comes as cases of the parasite have been confirmed less than 70 miles south of the United States–Mexico border.2

“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,” Ellen de Brabander, PhD, executive vice president of innovation and regulatory affairs at Elanco, said in an Elanco news release.1

The emergency use authorization of the isoxazoline provides veterinarians and pet owners with a treatment option should the parasite enter the US. According to Elanco, the FDA granted the authorization after evaluating a study on the efficacy of lotilaner against myiasis caused by NWS in naturally infested dogs.

The study, published in Parasites & Vectors, found that oral administration of lotilaner at the minimum recommended dosage in 11 infested dogs demonstrated 100% efficacy against Cochliomyia hominivorax (NWS) larvae within 24 hours of treatment.3

“Lotilaner demonstrated a rapid onset of action and a high efficacy against C hominivorax. We therefore recommend lotilaner for the effective treatment of myiasis in dogs,” the authors of the study wrote.3

Still, the data supporting lotilaner’s benefits against infestations caused by NWS larvae are limited. The study involved only 11 naturally infested dogs in Brazil, and its relevance to dogs in the US remains unknown. Researchers believe the primary mechanism of action against C hominivorax is the expulsion of live larvae. However, the combined use of mechanical removal and the absence of a control group make it difficult to isolate the drug’s specific effect, Elanco noted.1 The larval expulsion rate in the study was 80.5% at 2 hours post treatment and 93% at 6 hours post treatment, reaching 100% efficacy at 24 hours post treatment.3

Related: FDA conditionally approves drug to prevent and treat screwworm in cattle

A NWS infestation occurs when a NWS fly lays eggs on open wounds or other body parts of live, warm-blooded animals. The eggs hatch into larvae that then invade the tissues of the animal by burrowing themselves into wounds and feeding on the animal’s tissue.

According to the CDC, a small wound from a tick bite is enough to attract a female fly to feed and lay her eggs in it.4 One female can lay 200 to 300 eggs at a time and up to 3000 eggs over a 10- to 30-day lifespan.4

“Any break in the skin—from a scratch to a surgical incision—can become an entry point for NWS, due to its aggressive and invasive nature," said Casey Locklear, DVM, a Texas-based veterinarian and parasiticide lead at Elanco.1 "Preventing or rapidly treating existing wounds is critical to protecting pets from NWS. One way to limit self-inflicted scratching includes using year-round flea and tick protection, such as Credelio."

References

1. Elanco's Credelio (lotilaner) receives first ever FDA emergency use authorization (EUA) against New World screwworm (NWS) in dogs. News release. Elanco Animal Health. October 24, 2025. Accessed October 24, 2025. https://prnmedia.prnewswire.com/news-releases/elancos-credelio-lotilaner-receives-first-ever-fda-emergency-use-authorization-eua-against-new-world-screwworm-nws-in-dogs-302594317.html
2. Bautista-Alejandre A. New World screwworm detected less than 70 miles from the US-Mexico border. dvm360. September 22, 2025. Accessed October 24, 2025. https://www.dvm360.com/view/new-world-screwworm-detected-less-than-70-miles-from-the-us-mexico-border
3. do Vale TL, Costa AR, Miranda LM, et al. Efficacy of lotilaner against myiasis caused by Cochliomyia hominivorax (Diptera: Calliphoridae) in naturally infested dogs. Parasites & Vectors. 2023;16(1):86. doi:10.1186/s13071-023-05661-z
4. About New World screwworm. CDC. Accessed October 24, 2025. https://www.cdc.gov/new-world-screwworm/about/index.html