FDA conditionally approves combination parasiticide for New World screwworm

December 18, 2025

Credelio Quattro (Elanco) was previously approved by the FDA for treatment of infestation for 6 other parasites in dogs.

Officials with the FDA have granted conditional approval for a combination parasiticide to treat infestation of New World screwworm (NWS) larvae in dogs. The conditional approval expands the use of lotilaner, moxidectin, praziquantel and pyrantel chewable tablets (Credelio Quattro; Elanco), which was previously approved by the FDA for treatment of tick, flea, heartworm, roundworm, hookworm and tapeworm infestations.1

Screwworm fly

A drug is required to be shown as safe and have a reasonable expectation of effectiveness for it to be conditionally approved. According to Elanco, the FDA’s decision to grant conditional approval was based on a peer-reviewed study published in Parasites & Vectors that evaluated the efficacy of lotilaner against NWS.1

This study found lotilaner administered in a single dose was 100% effective against NWS larvae within 24 hours of treatment in dogs that were naturally infested with the parasite. The doses ranged from 23.9 mg/kg to 40.9 mg/kg body weight, and were based on the minimum manufacturer recommendation for control of fleas and ticks in dogs.1,2

“A rapid and efficient treatment is necessary to improve the recovery of affected animals and reduce the possibility of reinvasion in the areas where this parasitic fly has been eradicated,” the study’s authors wrote.2

RELATED: Communicating with clients about parasite protection

This study also weighed in earlier FDA decisions about lotilaner for treatment of NWS in companion animals. These decisions included issuing emergency use authorizations for lotilaner (Credelio; Elanco) to treat NWS in dogs, and lotilaner chewable tablets for cats (Credelio Cat; Elanco).3,4

“Elanco’s Credelio family of brands has made significant strides in animal health and this conditional approval for treatment of New World screwworm in dogs now allows us to provide multiple treatment solutions for veterinarians, animal shelters, and pet owners should they need it urgently,” Ellen DeBrander, PhD, executive vice president of research and development at Elanco, said in a news release.1

Earlier this year, NWS was confirmed less than 70 miles south of the US-Mexico border. This confirmation marked the northernmost detection of the parasite during the ongoing outbreak in Mexico. It prompted an increase in concern for animals in the US, particularly the cattle and livestock industry.5

In response to the NWS threat, the USDA has opened a sterile fly dispersal facility in Tampico, Mexico with a domestic facility at Moore Air Base in Edinburg, Texas, expected to open in early 2026, to help prevent infestation in the US.6 Additionally, the FDA has conditionally approved treatments for cattle.7,8

“We appreciate the FDA’s commitment to preparing and providing treatment options for New World screwworm in advance of the fly entering the US,” DeBrander said in the release.1

RELATED: Top questions on New World screwworm: What every veterinarian should know

References

  1. Elanco’s Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel chewable tablets) receives first FDA conditional approval for treatment of New World screwworm in dogs. News release. Elanco. December 18,2025. Accessed December 18,2025.
  2. do Vale TL, Costa AR, Miranda LM, et al. Efficacy of lotilaner against myiasis caused by Cochliomyia hominivorax (Diptera: Calliphoridae) in naturally infested dogs. Parasit Vectors. 2023;16(86). doi:10.1186/s13071-023-05661-z
  3. Bautista-Alejandre A. FDA grants emergency use authorization for lotilaner to treat New World screwworm in dogs. dvm360. October 24, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/fda-grants-emergency-use-authorization-for-lotilaner-to-treat-new-world-screwworm-in-dogs
  4. Bautista-Alejandre A. Antiparasitic receives FDA emergency authorization to treat New World screwworm in cats. dvm360. November 21, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/antiparasitic-receives-fda-emergency-authorization-to-treat-new-world-screwworm-in-cats
  5. Bautista-Alejandre A. New World screwworm detected less than 70 miles from the US-Mexico border. dvm360. September 22, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/new-world-screwworm-detected-less-than-70-miles-from-the-us-mexico-border
  6. Crossley KC. USDA opens sterile fly dispersal facility in Mexico. dvm360. November 14, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/usda-opens-sterile-fly-dispersal-facility-in-mexico
  7. Coppock Crossley K. FDA conditionally approves drug to prevent and treat screwworm in cattle. dvm360. September 30, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/fda-conditionally-approves-drug-to-prevent-and-treat-screwworm-in-cattle
  8. McCafferty. FDA conditionally approves topical drug for cattle to prevent and treat New World screwworm. dvm360. December 4, 2025. Accessed December 18, 2025. https://www.dvm360.com/view/fda-conditionally-approves-topical-drug-for-cattle-to-prevent-and-treat-new-world-screwworm
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