The U.S. Food and Drug Administration has issued an Emergency Use Authorization for generic nitenpyram tablets to treat New World screwworm infestations, or myiasis, in dogs and cats at least 4 weeks of age and weighing at least 2 pounds. This authorization marks the first generic animal drug approved for use against this concerning parasitic infection.
NWS flies lay eggs in open wounds or on mucous membranes. When the eggs hatch, the larvae burrow into living tissue, creating painful and potentially life-threatening wounds if left untreated. While most dogs and cats in the U.S. are at low risk, pets that live in or have recently traveled to areas with confirmed NWS cases are at higher risk of exposure.
At the time of publication, U.S. cases in farm animals had been reported in Texas and New Mexico. Only one incidence of canine infection had been reported in New Mexico.
Nitenpyram tablets kill most screwworm larvae within hours of administration. Affected pets should receive a second dose six hours after the first for best results. Because the drug has a short duration of action, it cannot prevent future infestations or protect against reinfestation.
The tablets are available over the counter in 11.4 milligram and 57 milligram strengths, with dosing based on the animal’s weight. The FDA noted that pet owners should seek veterinary care to safely remove remaining live or dead larvae and provide wound management to reduce the risk of infection and reinfestation.
Veterinarians recommending an emergency use-authorized product must inform clients that the product has not received full FDA approval for the treatment or prevention of NWS myiasis. Practitioners are also responsible for discussing potential risks, benefits, and available treatment alternatives with pet owners.
The FDA urges veterinarians to use authorized and conditionally approved antiparasitic products only when medically necessary. They warn that misuse or overuse of antiparasitic drugs could contribute to the development of resistance, a challenge that has been reported in some countries affected by NWS. Officials note that preserving the effectiveness of available treatments will be critical as efforts continue to prevent the establishment and spread of the parasite in the U.S.
Veterinary professionals can monitor NWS cases on the United States Department of Agriculture’s Animal and Plant Health Inspection Service’s website.