The FDA has granted Emergency Use Authorization (EUA) to Zoetis Inc.'s (ZTS) Simparica TRIO, a prescription chewable, for the treatment of New World screwworm in dogs and puppies, effective August 13, 2026. This is in addition to its existing indications and does not include preventative use. Based on the totality of scientific evidence, the FDA determined that the treatment is reasonably expected to be effective and that the potential benefits outweigh the risks. This proactive measure expands treatment options in the U.S., where detected cases are currently limited to parts of Texas and New Mexico.

Simparica TRIO is a combination product containing sarolaner, moxidectin, and pyrantel, which was initially approved by the FDA on February 27, 2020, for the prevention of heartworm and the treatment and control of fleas and ticks. Sarolaner, an isoxazoline, inhibits the gamma-aminobutyric acid (GABA) and glutamate-gated chloride channels in arthropods. Moxidectin acts on the glutamate-gated chloride channels of parasites, and pyrantel activates nicotinic acetylcholine receptors, leading to parasite paralysis. This EUA represents a repurposing of an already marketed product for an emergency indication, rather than relying on Phase 1, 2, or 3 clinical trial data. Due to the potential for tremors, ataxia, and seizures associated with isoxazolines, veterinary oversight and monitoring are required.

The competitive landscape for this indication has already shifted towards a multi-product approach. The FDA granted conditional approval to Elanco Animal Health's (ELAN) Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel) on December 17, 2025, and issued an EUA for Boehringer Ingelheim's NexGard (afoxolaner) on February 18, 2026. Furthermore, on June 11, 2026, a generic nitenpyram tablet, available over-the-counter, also received EUA for the treatment of dogs and cats, introducing price and accessibility competition. Simparica TRIO's strength lies in its ability to leverage its existing base of customers who already use a monthly combination dewormer and its established veterinary distribution network. Therefore, this action is more about reinforcing brand loyalty and ensuring continuity of treatment for existing customers than securing exclusive market access.

While Simparica TRIO generated global revenue of USD 1.194 billion in 2025, a 12% increase year-over-year, and the overall Simparica franchise reached USD 1.504 billion, the company states that Simparica TRIO is the world's leading canine parasiticide and has exceeded USD 1 billion in U.S. sales. However, the demand for New World screwworm treatment is currently limited to infected animals in specific regions, so the EUA itself is not a primary driver of short-term incremental revenue. The strategic value lies in incorporating a key brand into a national animal health portfolio that addresses a parasitic threat to the USD 113 billion U.S. cattle industry. This decision was made through the FDA's animal drug EUA review process, rather than requiring an advisory committee vote.