Merck Animal Health Secures FDA Conditional Approval for EXZOLT™ CATTLE-CA1—A Groundbreaking Tool Against New World Screwworm and Cattle Fever Tick
Merck Animal Health, known globally as MSD Animal Health outside the United States and Canada and a division of Merck & Co., Inc. announced today a significant regulatory milestone: the U.S. Food and Drug Administration (FDA) has granted conditional approval for EXZOLT™ CATTLE-CA1 (fluralaner topical solution). This innovative pour-on parasiticide represents the first novel ectoparasiticide for beef cattle in decades and is now conditionally approved for the prevention and treatment of infestations caused by New World screwworm (Cochliomyia hominivorax) larvae—a severe form of myiasis—and for the treatment and control of cattle fever tick (Rhipicephalus microplus).
The conditional approval comes at a critical time. The re-emergence and potential spread of New World screwworm—a parasitic fly whose larvae feed on the living tissue of warm-blooded animals—pose a renewed and escalating threat to U.S. livestock. Historically eradicated from the U.S. and much of Central America through a decades-long, binational eradication program, recent incursions in neighboring regions have reignited concerns among agricultural authorities, veterinarians, and cattle producers. Left unchecked, screwworm infestations can lead to animal suffering, high mortality rates, and staggering economic losses that experts estimate could reach hundreds of millions of dollars annually if the parasite becomes reestablished in the U.S.
“This threat is not hypothetical—it’s urgent,” said Rick DeLuca, President of Merck Animal Health. “EXZOLT CATTLE-CA1 is the first novel ectoparasiticide introduced for beef cattle in several decades. Its conditional approval underscores our deep commitment to delivering science-driven, innovative solutions that not only treat parasitic diseases but also help combat growing concerns around parasite resistance. By working closely with the FDA, we’ve accelerated access to a powerful new tool that will help veterinarians and cattle producers protect their herds, support sustainable farming practices, and safeguard the integrity of America’s beef supply chain.”
A New Class of Parasiticide for a Resurgent Threat
EXZOLT CATTLE-CA1 belongs to the isoxazoline class of parasiticides—a relatively new category of compounds known for their high potency and systemic activity against a wide range of external parasites. The active ingredient, fluralaner, works by selectively inhibiting the parasite’s nervous system, leading to rapid paralysis and death of the larvae or ticks upon ingestion.
Unlike traditional topical insecticides that remain on the skin surface, EXZOLT CATTLE-CA1 is formulated as a pour-on solution that is absorbed through the skin and distributed systemically throughout the animal’s body. This systemic action ensures that parasites feeding on the host—such as screwworm larvae burrowing into wounds or cattle fever ticks attaching to the hide—are effectively exposed to the active ingredient, even in hard-to-reach areas.
The conditional approval was granted based on comprehensive data demonstrating the safety of the product and a reasonable expectation of effectiveness when used according to label directions. These conclusions were drawn from global field and laboratory studies conducted by Merck Animal Health over recent years, which evaluated dosing regimens, efficacy against target parasites, and safety margins across various cattle populations.
Regulatory Innovation Enabling Rapid Response
The speed with which EXZOLT CATTLE-CA1 reached conditional approval reflects a collaborative and forward-thinking regulatory approach. The FDA’s expanded conditional approval pathway, coupled with the product’s designation as a priority zoonotic animal drug, allowed Merck Animal Health to bring this critical solution to market more rapidly than under traditional approval timelines.
“Without this regulatory flexibility, we simply could not have responded this quickly to an emerging agricultural threat,” explained Dr. Holger Lehmann, D.V.M., Ph.D., Vice President of Pharmaceutical Research & Development at Merck Animal Health. “This approval is a testament to what’s possible when industry and regulators align around a shared goal: protecting animal health, public health, and food security. Merck Animal Health has a long-standing legacy of innovation in parasite control, including robust stewardship programs to delay resistance development. EXZOLT CATTLE-CA1 is another step in that mission.”
Usage Guidelines and Availability
EXZOLT CATTLE-CA1 is approved for use in beef cattle two months of age and older, as well as in replacement dairy heifers under 20 months of age. However, it is not approved for use in bulls intended for breeding (one year and older), dairy calves, or veal calves. A 98-day meat withdrawal period must be observed before treated animals can be sent to slaughter, ensuring consumer safety.
Importantly, because this is a conditionally approved product, federal law strictly prohibits off-label or extra-label use. Veterinarians and producers must adhere precisely to the labeled indications, dosing instructions, and species restrictions.
The product will be available by prescription only, with launch planned for the first quarter of 2026 in 1-liter and 5-liter container sizes, facilitating use on both small and large operations.
Broader Regional Impact
The U.S. conditional approval follows closely on the heels of market authorization in Mexico, where EXZOLT CATTLE-CA1 has also been approved for the prevention and treatment of New World screwworm. This regional alignment is strategically significant, as coordinated cross-border parasite control is essential to preventing reinfestation and maintaining the hard-won gains of the decades-long screwworm eradication program.
A Vital Defense for the Future of U.S. Cattle Production
The conditional approval of EXZOLT CATTLE-CA1 arrives amid heightened vigilance from the USDA and state agricultural agencies. In recent years, isolated cases of New World screwworm have been detected in wildlife and livestock in areas near the U.S.-Mexico border, triggering emergency response protocols. The availability of a highly effective, systemically acting parasiticide gives veterinarians and producers a new line of defense—particularly valuable in outbreak scenarios or high-risk zones.
Moreover, the dual indication against cattle fever tick—a vector of bovine babesiosis, or “Texas fever”—adds further value. Cattle fever ticks are quarantined pests in the U.S., and infestations can lead to movement restrictions, costly treatments, and loss of market access. EXZOLT CATTLE-CA1’s activity against this tick species offers an additional layer of biosecurity for producers in endemic regions.
EXZOLT CATTLE-CA1 represents more than a new product—it is a strategic investment in the resilience of U.S. agriculture. By combining cutting-edge science, regulatory agility, and a deep understanding of producer needs, Merck Animal Health has delivered a timely and critical tool to combat two of the most economically damaging external parasites in cattle production.
As the industry faces evolving challenges—from climate-driven parasite range expansions to increasing resistance to older chemistries—innovations like EXZOLT CATTLE-CA1 will be essential to maintaining animal welfare, operational sustainability, and national food security. For more information about EXZOLT CATTLE-CA1, including full prescribing information, safety data, and availability updates, visit ExzoltCattle-CA1.com.
About Merck Animal Health
For more than a century, Merck, known as MSD outside the United States and Canada, has been inventing for life, bringing forward medicines and vaccines for many of the world’s most challenging diseases in human and animal health. Merck Animal Health is the global animal health business unit of Merck & Co., Inc., dedicated to preserving and improving health, well-being, and performance in animals through innovative solutions. With products available in more than 50 countries, the company serves veterinarians, farmers, pet owners, and governments worldwide. For more information, visit merck-animal-health.com.
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