FDA Approves Exzolt Cattle-CA1 for Prevention and Treatment of New World Screwworm
On December 4, 2025, the U.S. Food and Drug Administration (FDA) granted conditional approval to Exzolt Cattle-CA1, a fluralaner topical solution from Merck Animal Health, for the use in beef cattle (≥ 2 months of age) and replacement dairy heifers (< 20 months of age). The approved uses include prevention and treatment of larval infestations by New World screwworm (NWS), and treatment and control of cattle fever tick.
“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,” said Timothy Schell, director of the FDA’s Center for Veterinary Medicine, in a press release. “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.”
While NWS has not yet been detected in the U.S., the threat persists just south of the border with a new case being reported yesterday. Cattle fever ticks, present along the U.S.-Mexico border in south Texas, are competent vectors of Babesia bovis and Babesia bigemina — agents of bovine babesiosis (Texas cattle fever).
“The threat of New World screwworm represents a growing concern to U.S. agriculture, potentially causing devastating economic losses for cattle producers that could reach hundreds of millions of dollars,” said Rick DeLuca, president of Merck Animal Health, in a news release. “We worked closely with the FDA to accelerate availability so that veterinarians and cattle producers will have access to a powerful new tool to protect cattle from these serious parasites, helping to safeguard the industry’s economic future and the nation’s beef supply.”
The conditional approval status reflects FDA’s determination that Exzolt Cattle-CA1 is safe for its labeled use and is reasonably expected to be effective, while requiring that its sponsor, Merck Animal Health, submit further data demonstrating its effectiveness over the next five years to support full approval.
Administration and Use Considerations
Exzolt Cattle-CA1 is a ready-to-use, single-application pour-on that delivers the active ingredient, fluralaner, to act systemically against infestations. Administration involves applying a narrow band of the solution from between the shoulder blades to the tailhead. It will be available in the first quarter of 2026 by prescription in 250 mL, 1 L or 5 L bottles.
After administration, there is a 98-day withdrawal period before slaughter to ensure meat from treated animals is free of drug residues. Use is prohibited in lactating dairy cattle, dairy calves, veal calves or bulls over one year of age that are intended for breeding.
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This approval of Exzolt Cattle-CA1 complements that of Dectomax-CA1, which was authorized in September 2025 for prevention and treatment of NWS infestations in cattle. Together, these two products give veterinarians and producers their first pharmacologic defenses against NWS.
