Nitenpyram for Screwworm: What Has FDA Authorized?

What did the FDA authorize for dogs and cats?

The September 3 decision covers eligible adult animals, puppies and kittens. Generic Nitenpyram Tablets had previously received an emergency authorization for treatment alone in June. Adding prevention addresses a gap identified by the agency: earlier authorized or conditionally approved medicines for dogs and cats had focused on treating existing infestations. Both nitenpyram products are available without a prescription. [FDA announcement](https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-drugs-prevent-and-treat-new-world-screwworm-dogs-and-cats).

An emergency use authorization permits a specified use under emergency conditions; it does not establish full approval for that indication. FDA concluded that the available evidence supported a reasonable expectation of benefit and that the potential benefits outweighed the risks when the products were used as authorized. The agency uses several regulatory pathways to make animal treatments available, reflecting differences in products, species and supporting evidence. [FDA explanation of animal drug pathways](https://www.fda.gov/animal-veterinary/safety-health/animal-drugs-new-world-screwworm).

How does nitenpyram prevent and treat screwworm infestations?

Capstar's FDA fact sheet explains that prevention works by killing newly hatched larvae within 24 hours of dosing. The medicine does not repel adult flies, stop egg laying or prevent eggs from hatching. Preventive treatment therefore still requires attention to wounds and fly exposure. Owners should follow the product-specific instructions and consult their veterinarian about whether prevention is appropriate. [FDA Capstar fact sheet](https://www.fda.gov/media/194572/download).

The treatment evidence includes a small study published in Veterinary Parasitology in 2010. Correia and colleagues treated seven naturally infested beagles with nitenpyram; larvae were expelled from wounds, and remaining dead larvae were physically removed. This supports activity against the parasite, but the small sample limits confidence about outcomes across different animals and circumstances. Because the study treated existing infestations, it cannot independently establish how reliably a preventive regimen protects exposed pets. [Original nitenpyram study](https://pubmed.ncbi.nlm.nih.gov/20638181/).

Why does a pet with suspected screwworm need urgent veterinary care?

New World screwworm is the larval stage of the fly Cochliomyia hominivorax. Infestation, called myiasis, can damage healthy tissue as larvae burrow into wounds or body openings. FDA warns that the consequences in animals can be severe and potentially fatal. Visible maggots or a foul-smelling wound warrant immediate veterinary attention. [FDA animal health guidance](https://www.fda.gov/animal-veterinary/safety-health/animal-drugs-new-world-screwworm).

For established infestations, the Capstar instructions call for veterinary removal of remaining larvae alongside medication, with wound cleansing, removal of damaged tissue and pain management as needed. Pets can become reinfested, making protection from flies important until wounds heal. Owners should also report suspected adverse effects or treatment failure through their veterinarian, the manufacturer or FDA. [FDA treatment and safety instructions](https://www.fda.gov/media/194572/download).