Antiparasitic receives FDA emergency authorization to treat New World screwworm in cats

The FDA has issued an emergency use authorization for lotilaner chewable tablets (Credelio CAT; Elanco Animal Health) for treating New World screwworm (NWS) infestations in cats and kittens. Credelio CAT is the first drug to receive FDA authorization for the treatment of NWS in cats.¹

The emergency use authorization for Credelio CAT follows the earlier FDA authorization of lotilaner (Credelio) for treating New World screwworm infestations in dogs, which was announced on October 24.²

The FDA determined that, based on available scientific evidence, Credelio CAT may be effective in treating NWS infestations in cats and kittens. Although the product is not officially FDA-approved for treating NWS, the federal agency concluded that the known and potential benefits of the product outweigh its known and potential risks, clearing the way for its emergency use in affected animals.¹

The authorization was based on research evaluating Credelio CAT’s efficacy against naturally acquired Old World screwworm (OWS) myiasis in 2 cats in Malaysia, as well as studies of Credelio’s effectiveness against NWS myiasis in 11 naturally infested dogs in Brazil.^3-5 The latter study was the basis for the FDA’s emergency use authorization of Credelio for dogs earlier this fall.² According to the study on Credelio CAT, the treatment had 100% larvicidal effectiveness against OWS (Chrysomya bezziana) at 24 hours post-treatment in the 2 cats.⁴ Credelio also demonstrated 100% efficacy against the parasite’s larvae within 24 hours of treatment.⁵

“This historic [emergency use authorization] equips veterinarians and cat owners with a treatment solution and provides reassurance that they're prepared to act quickly if New World screwworm crosses into the US,” Ellen de Brabander, PhD, executive vice president of innovation and regulatory affairs at Elanco, said in a news release by Elanco.⁶

Credelio CAT is approved for flea and tick-related indications in cats and kittens. The product gained FDA approval for this use in 2019. Specifically, the product is approved for the treatment and prevention of flea infestations (Ctenocephalides felis) for one month in cats and kittens 8 weeks of age and older that weigh 2 lbs or more. The drug is also indicated for the treatment and control of infestations of Ixodes scapularis, commonly known as the black-legged tick, for one month in cats and kittens 6 months of age and older, weighing 2 lbs or more.⁷

As an isoxazoline, lotilaner use has been linked to neurologic adverse effects, such as muscle tremors, ataxia, and seizures. Veterinarians should take extra caution if using the product on cats with a history of neurologic disorders.²

The product is only available through a prescription from a licensed veterinarian as professional expertise is needed to monitor for and respond to possible adverse reactions.¹ Although NWS poses a low risk to most cats in the US, outdoor felines near the US-Mexico border or those that have traveled to countries with active NWS cases face a higher risk of NWS exposure.

On August 18, 2025, the Department of Health and Human Services declared NWS a potential for a public health emergency.⁸ According to an announcement by the FDA, the emergency use authorization for Credelio CAT to treat NWS in cats will be in place until it is revoked or until the Department of Health and Human Services declares that NWS no longer presents a significant potential for a public health emergency.¹

“Given [NWS's] aggressive and invasive nature, any minor wounds from grooming, scratching, or outdoor activities can serve as an entry point for these parasites," Casey Locklear, DVM, a Texas-based veterinarian and parasiticide lead at Elanco, said.⁶ "It's essential to prevent or quickly address any wounds to keep cats safe from [NWS].”

References

1. FDA Issues Emergency Use Authorization for Credelio CAT to Treat New World Screwworm in Cats. US Food and Drug Administration. November 21, 2025. Accessed November 21, 2025. https://content.govdelivery.com/accounts/USFDA/bulletins/3fc7c4b?reqfrom=share
2. Bautista-Alejandre A. FDA grants emergency use authorization for lotilaner to treat New World screwworm in dogs. dvm360. October 24, 2025. Accessed November 21, 2025. https://www.dvm360.com/view/fda-grants-emergency-use-authorization-for-lotilaner-to-treat-new-world-screwworm-in-dogs
3. Fact Sheet for Veterinarians: Emergency Use Authorization of Credelio™ CAT (lotilaner). US Food and Drug Administration. November 21, 2025. Accessed November 21, 2025. https://www.fda.gov/media/189726/download?attachment=&utm_medium=email&utm_source=govdelivery
4. Han HS, Yasmin L. Chrysomya bezziana (Diptera: Calliphoridae) infestation in two Malaysian cats treated with oral lotilaner. Vet Dermatol. 2020;31(4):335-e87. doi:10.1111/vde.12855
5. 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
6. Elanco's Credelio™ CAT (lotilaner) Receives First FDA Emergency Use Authorization (EUA) for Treatment of New World Screwworm (NWS) in Cats. News release. Elanco Animal Health. November 21, 2025. Accessed November 21, 2025.
7. FREEDOM OF INFORMATION (FOI) SUMMARY Original Emergency Use Authorization (EUA). November 21, 2025. Accessed November 21, 2025. https://www.fda.gov/media/189728/download?attachment=&utm_medium=email&utm_source=govdelivery
8. Declaration of Emergency Pursuant to the Federal Food, Drug, and Cosmetic Act for New World Screwworm. Department of Health and Human Services. August 20, 2025. Accessed November 21, 2025. https://www.federalregister.gov/documents/2025/08/20/2025-15918/declaration-of-emergency-pursuant-to-the-federal-food-drug-and-cosmetic-act-for-new-world-screwworm?utm_medium=email&utm_source=govdelivery