The US Food and Drug Administration (FDA) has issued an Emergency Use Authorisation (EUA) for Simparica TRIO (sarolaner, moxidectin and pyrantel chewable tablets) for the treatment of New World screwworm (NWS) infestations, or myiasis, in dogs and puppies.

Sponsored by Zoetis Inc., Simparica TRIO is authorised for the treatment of NWS infestations when used according to the conditions outlined in the EUA. The FDA said the product is not authorised for the prevention of New World screwworm.

The agency determined, based on the totality of available scientific evidence, that it is reasonable to believe Simparica TRIO may be effective in treating NWS myiasis in dogs and puppies. The FDA also concluded that the known and potential benefits of the product outweigh its known and potential risks when used as authorised.

New World screwworm is a parasitic infestation caused by the larvae of the Cochliomyia hominivorax fly. The larvae can infest wounds and body openings and feed on living tissue, potentially causing serious injury to affected animals.

Most dogs in the US are currently considered to have a low risk of exposure based on their geographic location. However, the FDA has advised owners of dogs that live in, travel to or return from areas where NWS infestations have been identified by federal or state animal health authorities, as well as certain countries south of the US border, to closely monitor their animals.

Signs of infestation can include visible maggots and foul odours from wounds or body openings, including the eyes, ears, nose and mouth. Dogs suspected of having an infestation should receive immediate veterinary attention.

The FDA noted that although isoxazoline products are widely used and considered safe for most dogs, they have been associated with neurological adverse reactions in some animals, including muscle tremors, loss of coordination and seizures. As a result, Simparica TRIO remains available only by prescription from a licensed veterinarian, who can assess whether the product is appropriate for an individual animal.

The EUA will remain effective until it is revoked or until the US Department of Health and Human Services terminates the declaration supporting emergency use of animal drugs for NWS.

The FDA said the authorization is part of efforts to ensure veterinarians have multiple treatment options should NWS infestations occur in US animals, while emphasising that current exposure risk remains geographically limited.