FDA emergency authorizes Capstar, generic nitenpyram to prevent and treat New World screwworm in dogs and cats

The FDA has authorized Capstar (nitenpyram) tablets and revised the emergency use authorization (EUA) for generic nitenpyram tablets to allow their use for both the prevention and treatment of New World screwworm (NWS) infestations in dogs and cats.¹

The agency announced the authorization September 3, marking the first time an FDA-authorized drug for dogs and cats has received an emergency-use indication for preventing NWS myiasis. The generic nitenpyram product was previously authorized in June for treatment only.^1,2

“Although the FDA has authorized or conditionally approved multiple products for the treatment of New World screwworm in dogs and cats, none were for prevention—until today,” Timothy Schell, PhD, director of the FDA’s Center for Veterinary Medicine, said in a statement.¹ “The FDA is addressing a previously unmet need and giving pet owners and veterinarians important tools to protect dogs and cats from NWS infestations.”

The EUAs apply to dogs, puppies, cats and kittens weighing at least 2 pounds and at least 4 weeks old. Both products are available over the counter in 11.4-mg and 57-mg tablets, with dosing based on body weight.¹

The FDA said its authorization is based on the totality of available scientific evidence. The agency concluded that it is reasonable to believe the products may be effective for prevention and treatment of NWS myiasis when used as authorized and that their known and potential benefits outweigh their known and potential risks.¹

New World screwworm, caused by the larvae of the parasitic fly Cochliomyia hominivorax, can infest warm-blooded animals, including pets. Female flies lay eggs in or around wounds or mucous membranes, and the resulting larvae feed on living tissue. Infestations can cause severe tissue damage and may be fatal if left untreated.

Most US pets remain at low risk, but animals traveling to affected areas should be monitored closely

Despite the new prevention option, the FDA said most dogs and cats in the US currently face a low risk of exposure, as confirmed NWS cases remain concentrated in a limited geographic area. Risk is higher for animals that live in, travel to or return from areas where state or federal animal health officials have identified NWS infestations, as well as certain countries south of the US border.

To date, there have been 48 domestic cases of NWS in goats, sheep, cattle, and 3 dogs.²

Veterinarians and pet owners should monitor at-risk animals for signs of infestation, including visible maggots or foul odors associated with wounds or body openings such as the eyes, ears, nose or mouth. Animals suspected of having an infestation should receive immediate veterinary care.¹

The FDA has emergency authorized or conditionally approved a growing number of animal drug products for NWS as federal officials respond to the reemergence of the parasite. The agency has issued 15 EUAs and 3 conditional approvals for animal drugs against NWS, as of today.

The EUAs for Capstar and Nitenpyram Tablets will remain in effect until they are revoked or until the US Department of Health and Human Services secretary terminates the declaration that circumstances exist justifying emergency use of animal drugs for NWS.¹

References

1. FDA issues emergency use authorization for drugs to prevent and treat New World screwworm in dogs and cats. News release. US Food and Drug Administration. September 3, 2026. Accessed September 3, 2026. https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-drugs-prevent-and-treat-new-world-screwworm-dogs-and-cats
2. FDA issues emergency use authorization for generic over-the-counter drug to treat New World screwworm in dogs and cats. US Food and Drug Administration. June 11, 2026. Accessed September 3, 2026. https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-generic-over-counter-drug-treat-new-world-screwworm-dogs-and
3. Confirmed detections of New World screwworm. US Department of Agriculture, Animal and Plant Health Inspection Service. Accessed September 3, 2026. https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/stop-screwworm/current-status/confirmed