FDA conditionally approves drug to prevent and treat screwworm in cattle

A new drug product for preventing and treating New World screwworm (NWS) larval infestations in cattle is conditionally approved by the FDA. Doramectin injection solution (Dectomax-CA1 Injectable; Zoetis) is also indicated for prevention of NWS reinfestation for 21 days in cattle.^1,2

FDA Commissioner Marty Makary, MD, MPH, said the conditional approval is the first in the US for NWS. “We understand the urgency with which America’s farmers and ranchers are asking for tools to fight [NWS],” Makary said in a news release.¹ “Today’s conditional approval shows our dedication to rapidly advancing important animal medicines when they are needed most. We continue to work tirelessly to complete review of other NWS products to protect multiple animal species in the US.”

NWS was recently confirmed less than 70 miles south of the US-Mexico border. This confirmation marks the northernmost detection of the parasite during the ongoing outbreak in Mexico and prompted an increase in concern for the US cattle and livestock industry.³

“The New World screwworm continues its March northward…Unlike typical maggots that feed on necrotic tissue, this screwworm larva loves living flesh. It will, in fact, disfigure and kill livestock, pets, wildlife, and yes, even you,” Christopher Lee, DVM, MPH, DACVPM, said in a Vet Watch update.⁴

Doramectin injection solution is indicated for use in beef cattle, female dairy cattle aged less than 20 months, pregnant beef cattle, newborn calves and bulls.² The drug is eligible for conditional approval because it aims to prevent and treat a serious or life-threatening disease in cattle and addresses an unmet animal health need. Eligibility was also determined because the drug requires complex or particularly difficult studies to demonstrate effectiveness.¹

“Under this conditional approval, the FDA has determined the drug is safe and has a reasonable expectation of effectiveness. We are making this treatment available to cattle producers immediately while the sponsor collects the data needed for a full approval,” Timothy Schell, PhD, acting director of the FDA’s Center for Veterinary Medicine, said in the release.¹ “The FDA will continue to expedite review of animal drugs to help the U.S. fight this devastating threat to our nation's livestock and the livelihoods of the farmers and ranchers who care for them."

Dectomax-CA1 contains the same active ingredient at the same dose as Zoetis’ Dectomax, which previously received full FDA approval for treatment and control of certain nematode and arthropod parasites in cattle and swine. The Dectomax approval included adequate target animal safety studies, manufacturing information, and human food safety information. This prior information submitted to the FDA negated the agency’s requirement for new information covering those aspects in support of the conditional approval for Dectomax-CA1.¹

The 35-day withdrawal period for cattle as well as warnings to prevent drug residues in meat from treated cattle are the same for Dectomax-CA1 as it is for Dectomax. However, a withdrawal period has not been established for this product in preruminating calves, and the FDA has advised against using the drug in calves that will be processed for veal.¹

“New World screwworm has the potential to bring unprecedented economic and animal health harm to livestock producers,” Mike Lormore, DVM, MS, MBA, director of cattle and pork technical services at Zoetis, said in a news release.² “Our top priority is to support keeping animals healthy and provide timely, efficacious solutions to our customers and partners. With this conditional approval, Dectomax-CA1 Injectable can now be used as part of safe, effective control measures against [NWS].”

Doramectin injectable solution is available in 250 mL and 500 mL bottles with a new label for Dectomax-CA1 anticipated to arrive in early 2026.^1,2 The label will contain both Dectomax and Dectomax-CA1 indications, although each drug has a unique application number, according to the FDA.¹ Zoetis is encouraging the implementation of strategic prevention and control measures by livestock producers working closely with herd veterinarians.²

References

1. FDA conditionally approves first drug for prevention and treatment of New World screwworm infestations in cattle. News release. FDA. September 30, 2025. Accessed September 30, 2025. https://www.fda.gov/news-events/press-announcements/fda-conditionally-approves-first-drug-prevention-and-treatment-new-world-screwworm-infestations
2. Zoetis receives conditional approval for Dectomax-CA1 injectable for the prevention and treatment of New World screwworm myiasis in cattle. News release. Zoetis. September 30, 2025. Accessed September 30, 2025. https://investor.zoetis.com/news/news-details/2025/Zoetis-Receives-Conditional-Approval-for-Dectomax-CA1-Injectable-for-the-Prevention-and-Treatment-of-New-World-Screwworm-Myiasis-in-Cattle/default.aspx
3. Bautista-Alejandre A. New World screwworm detected less than 70 miles from the US-Mexico border. dvm360. September 22, 2025. Accessed September 30, 2025. https://www.dvm360.com/view/new-world-screwworm-detected-less-than-70-miles-from-the-us-mexico-border
4. Lee C. New World screwworm invasion update; a looming threat to US borders. Vet Watch. July 15, 2025. Accessed September 30, 2025. https://www.dvm360.com/view/new-world-screwworm-invasion-update-a-looming-threat-to-us-borders