Full Breakdown

FDA Issues Emergency Use Authorization for Simparica Trio Chew to Treat New World Screwworm in Dogs

8/14/2026, 2:56:02 AM

Core Event: EUA Granted for Simparica Trio

On August 13, Zoetis announced that its monthly chewable product Simparica Trio (sarolaner, moxidectin, pyrantel) received an Emergency Use Authorization (EUA) from the FDA for treating New World screwworm (*Cochliomyia hominivorax*) infestations in puppies and dogs.

New World screwworm larvae feed on living tissue, causing severe pain, rapid tissue loss, and possible death. Recent spread has led several U.S. states to require treatment of domestic animals before crossing state lines from infested areas, according to USDA APHIS data. Veterinarians are urged to report suspicious wounds, visible maggots, or other signs promptly.

Confirmed detections are limited to specific regions of Texas and New Mexico. Most U.S. dogs are at low risk, but those living in, traveling to, or returning from these zones should be monitored. The EUA applies only to treatment, not prevention, and remains in effect until the emergency declaration ends.

Acting FDA Commissioner Kyle Diamantas said the authorization adds a treatment option, noting that the FDA believes the known and potential benefits outweigh the risks.

Abhay Nayak, EVP and President of U.S. Commercial Operations at Zoetis, called the EUA a simplification for veterinarians, allowing a single monthly chew to address routine parasite protection and emergent screwworm infestations.

Timothy Schell, Ph.D., director of the FDA’s Center for Veterinary Medicine, urged owners to stay informed about signs of infestation and consult veterinarians.

The FDA flagged that isoxazoline drugs, including sarolaner, have been linked to neurologic reactions such as tremors, ataxia, and seizures in dogs. The most common side effects in trials were vomiting and diarrhea. The product is not evaluated for breeding, pregnant, or lactating dogs and should be used cautiously in animals with a seizure history. Simparica Trio remains prescription-only and is already approved for heartworm, flea, and tick protection.

In a separate EUA, the FDA authorized CLiK Extra wound spray for prevention of New World screwworm in livestock and captive wildlife, including sheep, cattle, goats, swine, llamas, alpacas, camels, deer, elk, and American bison. The spray acts as an insect-growth regulator, disrupting larval development. It is available over the counter for topical use, but the authorization covers prevention only; treatment of existing infestations requires veterinary care.

The Simparica Trio EUA gives veterinarians a ready-to-use, single-dose option that fits into existing monthly parasite-control regimens.

For livestock producers, the CLiK Extra spray provides a preventive measure that can be applied during routine procedures, helping limit parasite spread across animal populations.

The Simparica Trio EUA will remain active until the emergency declaration is revoked by HHS. Ongoing monitoring of case reports and adverse-event data will guide any future adjustments.