The Food and Drug Administration has authorized Capstar, a nitenpyram tablet long sold over the counter for flea control, to prevent and treat New World screwworm in dogs and cats. The September 3 action is an Emergency Use Authorization rather than a full drug approval, and it also revises an earlier authorization for generic nitenpyram so that it covers prevention as well as treatment.
For pet owners, the practical change is that a familiar brand is now covered. The tablets can be bought without a prescription, in two sizes, with dosing set by the animal’s weight, and the authorization now names prevention alongside treatment for the first time.
Scope of the emergency authorization
According to the FDA announcement, two products are covered: Capstar, made by Sergeant’s Pet Care Products of Omaha, Nebraska, and generic Nitenpyram Tablets from Felix Pharmaceuticals of Ireland. Both come in 11.4 mg and 57 mg tablets and are authorized for dogs, puppies, cats and kittens weighing at least 2 pounds and at least 4 weeks old. Animals below those limits are outside the authorization.
The authorization rests on the agency’s finding that the known and potential benefits outweigh the known and potential risks, and it remains in effect until it is revoked or the Secretary of Health and Human Services terminates the underlying emergency declaration. Timothy Schell, Ph.D., director of the FDA’s Center for Veterinary Medicine, said: “The FDA is addressing a previously unmet need and giving pet owners and veterinarians important tools to protect dogs and cats from NWS infestations.”
Trade coverage in dvm360 describes the action as the first FDA-authorized prevention option for the parasite in companion animals, and quotes the agency’s conclusion that it is “reasonable to believe the products may be effective for prevention and treatment of NWS myiasis.” That wording is the emergency-use standard, which is lower than the evidence of effectiveness needed for a full approval.
How this differs from earlier screwworm drugs
The generic version arrived first. In a June 11 notice from USDA’s Animal and Plant Health Inspection Service, the agency described the generic nitenpyram authorization for treatment as the first generic animal drug authorized for use against the parasite. The September action extends that to prevention and adds the brand-name Capstar.
Before that, the FDA’s February 18 authorization for NexGard (afoxolaner) covered dogs only, for treatment only, and only by prescription. That document says the agency needed more information to evaluate NexGard for prevention, and that the drug should be used together with mechanical removal of larvae from wounds. Against that background, the September action is notable for three things at once: a widely stocked brand name, coverage of cats and dogs, and a prevention claim that no earlier authorization made.
The limits carry over as well. Emergency use authorization is tied to a declaration, so the tablets are authorized “for this use only” while the emergency stands, in the words the FDA used for the NexGard authorization. Nothing in the September announcement changes the age and weight floor, and nothing tells owners to give the tablets to an animal that has no exposure risk.
Who actually needs it, and when to skip the pill
Risk is not evenly spread. FDA and APHIS both say most dogs and cats in the United States face low risk, and that risk is elevated for pets in areas with confirmed cases or for those traveling south of the U.S. border. Medical Daily’s explainer lists pets that travel to affected regions, are imported from Mexico or Central America, live in confirmed outbreak areas or cross the southern border with their owners as the groups at higher risk.
The same explainer stresses that an active infestation needs a veterinarian, not home medication. Warning signs include a worsening wound, visible maggots, a foul odor near a wound or body opening, pain and loss of appetite. It also cautions owners who know nitenpyram from flea control not to assume familiar flea-treatment dosing applies, and to consult the screwworm-specific fact sheet, since the dose is set by the animal’s weight.
The APHIS notice put the same point in its own words: most dogs and cats across the United States face low risk, though it said risk is “elevated for pets recently in areas with confirmed cases of NWS.” The parasite was eradicated from the United States decades ago and has moved north through Central America into Mexico, according to Medical Daily, which is why the border features so heavily in the guidance. Pets that stay in areas without confirmed cases have little reason to seek out the tablets.
Whether the authorization changes outcomes will depend on data not yet published. The FDA has not released case counts for pets treated under the emergency-use terms, and the authorization stays in force only as long as the HHS emergency declaration does.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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