FDA authorizes Simparica Trio for treatment of NWS myiasis

The FDA has issued an emergency use authorization (EUA) for sarolaner, moxidectin, and pyrantel chewable tablets (Simparica Trio; Zoetis), allowing the product to be used for the treatment of New World screwworm (NWS) myiasis in dogs and puppies.¹ The authorization is limited to treatment and Simparica Trio is not authorized under the EUA for NWS prevention.

According to the FDA, the agency reviewed the totality of the currently available scientific evidence and determined that Simparica Trio may be effective for treating NWS infestations in eligible dogs and puppies, and that the product's known and potential benefits outweigh its known and potential risks for that use.¹ As with the agency's other NWS-related EUAs, Simparica Trio will be available by prescription only from licensed veterinarians for as long as the EUA remains in effect, unless it is terminated or revoked sooner.

Timothy Schell, PhD, director of the FDA's Center for Veterinary Medicine, emphasized that most dogs in the US currently face a low risk of NWS exposure, given that confirmed detections remain limited to specific areas of Texas and New Mexico. "The best thing dog owners can do right now is stay aware of the situation, know the signs of infestation, and have a conversation with their veterinarian," Schell said.¹

Recognizing NWS myiasis

NWS is caused by the larvae of the NWS fly (Cochliomyia hominivorax), which lay eggs in open wounds or mucous membranes; the resulting larvae feed on living tissue, a condition known as myiasis. The FDA noted that signs of infestation can include visible maggots or a foul odor emanating from a wound or body opening.¹ Veterinarians practicing in or near affected regions or treating dogs that have recently traveled south of the US border are encouraged to maintain a high index of suspicion and report suspected cases through appropriate state and federal channels.

The current EUA adds to a growing list of NWS-related authorizations the FDA has issued for use in various species since the parasite's advance toward, and eventual detection within, the US.² Simparica Trio's addition gives veterinarians another option specifically labeled for use in dogs and puppies already being treated with the product for other parasites.

About the product

Simparica Trio combines 3 active ingredients: sarolaner, an isoxazoline-class parasiticide; moxidectin; and pyrantel. The combination product already carries FDA approval for the prevention of heartworm disease and the treatment and control of flea and tick infestations and roundworm and hookworm infections in dogs and puppies. The NWS treatment indication authorized under the EUA is in addition to, not a replacement for, those existing approved uses.

Because sarolaner belongs to the isoxazoline class, veterinarians should continue to counsel clients on the class's associated risks. Isoxazoline products have been associated with neurologic adverse reactions, including muscle tremors, ataxia, and seizures, in some dogs, even those without a prior history of seizures.¹ Practitioners are encouraged to discuss a patient's full medical history before prescribing.

“The FDA continues to authorize products to give veterinarians and pet owners multiple treatment options, in the unlikely event animals under their care become infested with New World screwworm,” said acting FDA commissioner Kyle Diamantas, JD. “To date, the US has been successful in containing the spread of NWS. We are hopeful it will remain that way, and by authorizing products like this, the US will be ready if the need arises.”

References

1. FDA issues emergency use authorization for drug to treat New World screwworm in dogs and puppies. FDA. August 13, 2026. Accessed August 13, 2026. https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-drug-treat-new-world-screwworm-dogs-and-puppies
2. Animal drugs for New World screwworm. FDA. Accessed August 13, 2026. https://www.fda.gov/animal-veterinary/safety-health/animal-drugs-new-world-screwworm