FDA expands animal drug options for New World screwworm treatment and prevention
The FDA has expanded animal drug options for New World screwworm through conditional approvals and emergency use authorizations. The agency lists products for cattle, dogs and cats and says its guidance page will be updated as more drugs move through the system.
The Food and Drug Administration has expanded the animal drug options available for the prevention or treatment of New World screwworm myiasis through conditional approvals and emergency use authorizations. The agency says its Center for Veterinary Medicine is working with animal drug sponsors to identify products and move them through approval or other authorization routes, and that its New World screwworm page is designed as a working reference that will be updated as new information becomes available.
The agency says three animal drugs are currently listed as approved or conditionally approved for New World screwworm: Dectomax-CA1 for cattle, Exzolt Cattle-CA1 for cattle, and Credelio Quattro-CA1 for dogs and puppies. The listed indications cover prevention, treatment, or both, depending on the product. Additionally, the FDA has granted conditional approval for Dectomax-CA1, a doramectin injectable solution, for cattle; Exzolt Cattle-CA1, a fluralaner topical solution, for beef cattle 2 months of age and older and replacement dairy heifers less than 20 months of age; and Credelio Quattro-CA1, monthly chewable tablets with the active ingredients lotilaner, moxidectin, praziquantel, and pyrantel, for dogs and puppies at least 8 weeks of age and weighing at least 3.3 pounds.
On September 30, 2025, Dectomax-CA1 was the first product to receive conditional approval for the prevention and treatment of infestations caused by larvae of Cochliomyia hominivorax and prevention of reinfestation for 21 days in cattle. The conditional dose is 1 mL (10 mg doramectin) per 110 lb of body weight administered by subcutaneous or intramuscular injection in the neck region. There is no change to the previously established pre-slaughter withdrawal period of 35 days.
The Department of Health and Human Services issued a declaration on August 18, 2025, that enables the agency to issue Emergency Use Authorizations for animal drugs to treat or prevent infestations caused by New World screwworm. On February 18, the FDA issued emergency use authorizations for NexGard chewable tablets to treat New World screwworm larvae infestations in dogs and puppies and NexGard COMBO to treat larvae infestations in cats and kittens. The FDA said it is reasonable to believe that NexGard and NexGard COMBO may be effective in the treatment of New World screwworm myiasis in dogs and puppies and cats and kittens, respectively, and that known and potential benefits of using the medications offlabel outweigh the known and potential risks.
NexGard chewable tablets contain the active ingredient afoxolaner, are given orally at the minimum dosage of 1.14 mg/lb (2.5 mg/kg), and should be used in conjunction with the mechanical removal of larvae remaining in the wound after treatment. NexGard COMBO is a topical medication with the active ingredients esafoxolaner, eprinomectin, and praziquantel. It is dosed at a minimum of 0.055 mL/lb (0.12 mL/kg) and should be applied topically according to body weight. When used to treat New World screwworm larvae infestations, these drugs should be used in conjunction with the mechanical removal of larvae, live and dead, remaining in the wound after treatment.
Since 2025, the FDA has granted emergency use authorizations for three other animal drugs for treatment of New World screwworm infestations: Credelio chewable tablets for dogs and puppies, Credelio CAT chewable tablets for cats and kittens, and Ivomec injectable solution for cattle. Credelio was authorized on October 24, 2025, for dogs and puppies 8 weeks and older, and Credelio CAT was authorized on November 21, 2025, for cats and kittens 8 weeks and older. Ivomec was granted emergency use authorization status on February 5 for preventing myiasis caused by screwworm larvae when administered within 24 hours of birth, at the time of castration, or when a wound appears.
The current FDA list of emergency-authorized products also includes F10 Antiseptic Wound Spray with Insecticide for several species. Ivomec is not authorized for use in lactating dairy cattle producing milk for human consumption or in calves intended for veal, and cattle treated under the emergency use authorization are subject to a 35-day slaughter withdrawal period. The FDA emphasized that antiparasitic drugs should be used judiciously and as part of a broader parasite management strategy to reduce the risk of resistance.
The FDA also reminds veterinarians that extralabel use can be allowed under existing regulations and within a valid veterinarian-client-patient relationship, but it is limited to drugs with full FDA approval. It does not include conditional approvals, index listed products, or products being used under an emergency use authorization. The agency points to 21 CFR Part 530 and says the page will be updated as more drugs are approved, conditionally approved, or otherwise authorized for this use.