FDA Conditionally Approves Elanco Drug for Screwworm in Dogs

The FDA has conditionally approved Elanco Animal Health’s Credelio Quattro-CA1 for the treatment of infestations caused by New World screwworm larvae in dogs, marking the first conditional approval for a companion animal product targeting the parasite.

The approval allows the drug to be used while Elanco completes additional studies required for full approval, expanding treatment options as New World screwworm cases have been detected in Mexico closer to the U.S. border. “We appreciate the FDA’s commitment to preparing and providing treatment options for New World screwworm in advance of the fly entering the United States,” said Ellen DeBrander, Executive Vice President of R&D, Elanco.

New World screwworm, Cochliomyia hominivorax, is a parasitic fly whose larvae infest open wounds in warm-blooded animals, feeding on living tissue and causing myiasis. The parasite primarily affects livestock but can also infest pets, wildlife and humans. While the United States eradicated the fly decades ago, it remains present in parts of Latin America, including Mexico.

According to the US Department of Agriculture, 14 cases of New World screwworm have been reported within 400 miles of the US–Mexico border, all associated with cattle movement. Mexican authorities have confirmed detections as close as 70 miles south of the border. While most dogs in the United States are considered at low risk due to geographic factors, the FDA said dogs near the US–Mexico border or dogs that have traveled to countries with active infestations face a higher risk of exposure.

Credelio Quattro-CA1 is a flavored chewable tablet that combines lotilaner, moxidectin, praziquantel and pyrantel. The FDA’s conditional approval applies to dogs and puppies at least eight weeks old and weighing at least 3.3 pounds. Under the conditional approval framework, the agency has determined that the drug is safe and has a reasonable expectation of effectiveness for its intended use. Elanco has up to five years to submit additional effectiveness data to support a full approval.

The FDA said Credelio Quattro-CA1 qualified for conditional approval because it is intended to treat a serious or life-threatening disease, addresses an unmet animal health need and would require complex or difficult studies to fully demonstrate effectiveness. The application received expedited review through the Priority Zoonotic Animal Drug designation, an authority established under the CARES Act.

Data supporting the approval include a peer-reviewed study published in Parasites & Vectors evaluating lotilaner, one of the drug’s active ingredients. In that study, oral administration of lotilaner at the minimum recommended dose demonstrated 100% efficacy against New World screwworm larvae within 24 hours in naturally infested dogs. The FDA defines conditional approval as evidence of safety combined with a reasonable expectation of effectiveness.

The approval adds to existing regulatory actions involving Elanco’s Credelio products. Credelio and Credelio CAT previously received Emergency Use Authorizations from the FDA for the treatment of New World screwworm infestations in dogs and cats, respectively. Emergency use authorizations permit temporary use of approved products for unapproved indications during declared circumstances, while conditional approval allows broader availability pending additional data.

Credelio Quattro, which is already fully approved by the FDA for flea, tick and worm-related indications, contains the same four active ingredients at the same doses as Credelio Quattro-CA1. Each product has a separate application number, but Elanco said product labeling beginning in 2026 will reflect both sets of indications on the same package.

With the conditional approval, Credelio Quattro-CA1 expands the product’s parasite coverage to include treatment of New World screwworm larvae in addition to ticks, fleas, heartworm disease, roundworms, hookworms and tapeworms. Elanco said the approval represents the third label update for the Credelio Quattro brand since its launch earlier this year.

The drug will be available by prescription only. The FDA said professional veterinary oversight is required due to potential adverse reactions. Lotilaner belongs to the isoxazoline class of antiparasitic drugs, which have been associated with neurologic adverse events, including tremors, incoordination and seizures in some dogs. The agency advises veterinarians and pet owners to assess whether the drug is appropriate for individual animals.

As detections of New World screwworm continue to be reported in Mexico, US regulators and animal health companies have emphasized treatment availability for companion animals should exposure occur, particularly in regions with closer proximity to confirmed cases.