FDA conditionally approves topical drug for cattle to prevent and treat New World screwworm

The FDA announced that it has conditionally approved fluralaner topical solution (Exzolt Cattle-CA1; Intervet Inc) for preventing and treating New World screwworm (NWS) larval infestations. The product is also indicated for treating and controlling cattle fever ticks in beef cattle older than 2 months and replacement dairy heifers younger than 20 months.

By receiving conditional approval, fluralaner topical solution was determined by the FDA to be safe and have a reasonable expectation of effectiveness for its intended use. The product's sponsor, Intervet Inc., from Rahway, New Jersey, has up to 5 years to generate the additional effectiveness data the FDA needs to support a full approval.1

“The FDA is leveraging every resource and authority at its disposal to ensure producers and veterinarians have the critical products they need to protect their livestock and safeguard our food supply against NWS and cattle fever tick,” Timothy Schell, PhD, director of the FDA’s Center for Veterinary Medicine, said in an organizational release.1 “We remain steadfast in our commitment to ensuring that animal drugs are safe and effective and that food from treated animals is safe to eat.”

Per FDA standards, fluralaner topical solution became eligible for conditional approval because it is intended to prevent and treat a serious or life-threatening illness in cattle, demonstrating the effectiveness of the drug requires complex or particularly difficult studies, and addresses an unmet animal health need. The treatment also received an expedited review through a priority zoonotic animal designation, which is authority given to the FDA under the Coronavirus Aid, Relief, and Economic Security Act.

RELATED: Top questions on New World screwworm: What every veterinarian should know2

The slaughter withdrawal period for fluralaner topical solution is 98 days to prevent unsafe drug residues in meat from treated cattle, as well as to ensure human food safety.1 The FDA also stated that this product is not for use in lactating dairy cattle, dairy calves, veal calves, or bulls that are at least aged 1 year and intended for breeding.

“This conditional approval gives cattle producers a new tool to combat two parasites threatening the well-being of cattle in the U.S.,”  FDA Commissioner Marty Makary, MD, MPH, said in a news release.1 “Although NWS has not been detected in the U.S., cattle fever tick is here. This is the first drug conditionally approved by the FDA specifically for the control and treatment of cattle fever tick.”

Intervet's fluralaner topical solution is available only by prescription and is offered in 250-mL, 1-L, and 5-L bottles. It is a single-use, ready-to-use product that is applied directly to the hair and skin in a narrow strip extending along the patient’s back, from between the shoulder blades to the base of the tail.

Other recent NWS treatment announcements

Lotilaner (Credelio; Elanco Animal Health) received emergency use authorization from the FDA to treat NWS infestations in dogs, the first time the FDA granted this authorization for both canine patients and any animal drug. A study published in Parasites & Vectors found that oral administration of lotilaner at the minimum recommended dose demonstrated 100% efficacy against NWS larvae within 24 hours of treatment when tested in 11 dogs infested with the parasite.3

In November 2025, the FDA issued an emergency use authorization for lotilaner chewable tablets (Credelio Cat; Elanco Animal Health) for treating NWS infestations in cats and kittens, making it the first drug to receive authorization from the FDA for treatment of NWS in feline patients.4

“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.5

Lotilaner is an isoxazoline that has been linked to neurologic adverse effects, including ataxia, muscle tremors, and seizures. Veterinarians should be cautious when using this product on feline patients with a history of neurologic disorders. Currently, there is a low risk to most cats in the US from NWS; however, outdoor cats near the US-Mexico border or those that have traveled to countries with active NWS cases face a higher risk of exposure. Although proven efficacy, the data are limited because the study involved only 11 naturally infected dogs in Brazil, so its relevance to canines in the US is unknown.

Doramectin injection solution (Dectomax-CA1 Injectable; Zoetis) received conditional approval in September 2025 to prevent and treat NWS larval infestations in cattle, and was indicated for the prevention of reinfestation for 21 days in cattle.6 The injection solution is indicated for use in beef cattle, female dairy cattle younger than 20 months, pregnant beef cattle, newborn calves, and bulls. The active ingredient in Dectomax-CA1 is the same dose as in Dectomax, which has received full FDA approval for treating and controlling certain nematode and arthropod parasites in cattle and swine.

Reference

1. FDA conditionally approves topical drug for cattle for New World Screwworm and cattle fever tick. News release. FDA. December 4, 2025. Accessed December 4, 2025. https://www.fda.gov/news-events/press-announcements/fda-conditionally-approves-topical-drug-cattle-new-world-screwworm-and-cattle-fever-tick?utm_medium=email&utm_source=govdelivery
2. Alaburda B. Top questions on New World screwworm: What every veterinarian should know. dvm360. December 1, 2025. Accessed December 4, 2025. https://www.dvm360.com/view/top-questions-on-new-world-screwworm-what-every-veterinarian-should-know
3. Bautista-Alejandre A. FDA grants emergency use authorization for lotilaner to treat New World screwworm in dogs. dvm360. October 24, 2025. Accessed December 4, 2025. https://www.dvm360.com/view/fda-grants-emergency-use-authorization-for-lotilaner-to-treat-new-world-screwworm-in-dogs
4. Bautista-Alejandre A. Antiparasitic receives FDA emergency authorization to treat New World screwworm in cats. dvm360. November 21, 2025. Accessed December 4, 2025. https://www.dvm360.com/view/antiparasitic-receives-fda-emergency-authorization-to-treat-new-world-screwworm-in-cats
5. 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. https://investor.elanco.com/press-releases/press-releases-details/2025/Elancos-Credelio-CAT-lotilaner-Receives-First-FDA-Emergency-Use-Authorization-EUA-for-Treatment-of-New-World-Screwworm-NWS-in-Cats/default.aspx
6. Coppock Crossley K. FDA conditionally approves drug to prevent and treat screwworm in cattle. dvm360. September 30, 2025. Accessed December 4, 2025. https://www.dvm360.com/view/fda-conditionally-approves-drug-to-prevent-and-treat-screwworm-in-cattle