FDA Issues Emergency Use Authorization for Topical Powder to Prevent and Treat New World Screwworm in Multiple Species

April 27, 2026

Today, the U.S. Food and Drug Administration issued an Emergency Use Authorization (EUA) for Negasunt Powder (coumaphos, propoxur, and sulfanilamide topical powder) for the prevention and treatment of New World screwworm (NWS) infestations (myiasis).

The FDA has concluded that based on the scientific evidence available, it is reasonable to believe that Negasunt Powder may be effective for the prevention and treatment of NWS myiasis in cattle, swine, goats, sheep, horses, donkeys, domestic hybrid equids (e.g., mules), and captive wild, exotic, and zoo mammals, and that the known and potential benefits of the product outweigh its known and potential risks.

Currently, Elanco US Inc., the drug sponsor, intends to limit distribution of Negasunt Powder to the U.S. Department of Agriculture (USDA) for further distribution to authorized users. Prior to an incursion of NWS into the U.S., Negasunt Powder is only available for use by employees of federal, state, local, and federally recognized tribal agencies, and people working under their authority and at their direction. If there is an incursion of NWS into the U.S., the product may also be used by or on the order of a licensed veterinarian in NWS-infested zones and adjacent surveillance zones as defined by the USDA in the NWS Response Playbook (page 9). There are no NWS-infested zones in the U.S. because, to date, NWS is not currently in the U.S.

Coumaphos and propoxur, two of the active ingredients in Negasunt Powder, can cause neurotoxicity. The EUA sets specific requirements to address this risk for people, animals, and the environment.

It is important that authorized users of this product review all human and animal safety information, including the boxed warning and limitations of authorized use, and closely follow its conditions of use and disposal instructions as detailed in the Fact Sheet: Emergency Use Authorization of Negasunt Powder (coumaphos, propoxur, and sulfanilamide topical powder) for New World Screwworm (NWS).

Food safety information:

Treated animals must not be slaughtered for human consumption within 28 days of the last treatment.
A milk discard time has not been established for this product; do not use in animals producing milk for human consumption.
A withdrawal period has not been established for this product in pre-ruminating calves; treated calves and calves born to treated cows must not be processed for veal.

This EUA will be effective until it is revoked or the HHS Secretary terminates the declaration that the potential public health emergency presented by NWS justifies the emergency use authorization of animal drugs for NWS.

Negasunt Powder is sponsored by Elanco US Inc. based in Indianapolis, Indiana.

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