FDA approves emergency use of generic ivermectin to prevent New World screwworm in cattle

The FDA has issued an emergency use authorization (EUA) for ivermectin (Bimectin) injection to prevent New World screwworm (NWS) infestations, or myiasis, in cattle.¹ The drug is authorized for administration within 24 hours of birth, at the time of castration, or at the appearance of a wound.

Bimectin is the agency's 14th EUA against NWS,¹ as the number of confirmed detections of the flesh-eating parasite in animals continues growing in Texas. To date, the USDA has confirmed 47 domestic cases of New World screwworm in animals, including in 3 dogs.²

Bimectin injection is a generic version of Ivomec, which the FDA authorized in February 2026 for NWS prevention in cattle. The authorization applies only to the injectable form and does not cover other dosage forms. It is also not authorized for use in lactating dairy cows or in calves that will be processed for veal, and cattle producers must observe a 35-day slaughter withdrawal time to avoid drug residues in the food supply.

The product is available over the counter without a prescription.

"By authorizing both generic and pioneer products, the Agency is ensuring producers aren't dependent on a single manufacturer or product to protect their herds,” Timothy Schell, PhD, director of the FDA's Center for Veterinary Medicine, said in an FDA announcement.¹

The FDA did not require new bioequivalence, target animal safety, or human food safety studies for the authorization, as Bimectin injection contains the same active ingredient at the same concentration and dosage form as Ivomec and is administered to the same species and class at the same dose and route.³ The agency instead grounded its effectiveness determination in Bimectin injection's established bioequivalence to Ivomec and in studies conducted with ivermectin injection.³

That evidence includes four dose confirmation studies conducted in Brazil and Argentina in 1991 and 1992, in which no calves treated with a single 200-mcg/kg dose developed myiasis requiring rescue treatment, while untreated controls developed infestations within the first week of birth or castration.³

Published literature from 1993 to 2022 showed variable but supportive results; the agency noted that effectiveness figures differed across studies but collectively supported a reasonable belief that the product may be effective when used as authorized.³

According to the FDA’s Freedom of Information document, the agency determined that the known and potential benefits of Bimectin injection outweigh its known and potential risks, noting that untreated New World screwworm infestations can be fatal because of tissue damage caused by the larvae.³

Bimectin injection joins a small set of products already cleared against NWS in cattle: a conditionally approved injectable, Dectomax-CA1 (doramectin injection), and a conditionally approved topical, Exzolt Cattle-CA1 (fluralaner). The FDA determined that neither the conditionally approved injectable nor the conditionally approved topical is an adequate alternative to an over-the-counter generic.

According to the agency, the conditionally approved injectable cannot be produced in sufficient quantities to meet the demands of a widescale incursion, while the conditionally approved topical belongs to a different pharmacological class, requires a prescription, and is restricted to cattle 2 months and older.³

The EUA will remain in effect until it is revoked or the Secretary of Health and Human Services ends the emergency declaration that allows the FDA to authorize animal drugs for NWS, the FDA said. Bimectin injection is sponsored by Ireland-based Bimeda Animal Health Ltd.

References

1. FDA issues emergency use authorization for generic drug to prevent New World screwworm in cattle. News release. US Food and Drug Administration. August 27, 2026. Accessed August 27, 2026. https://www.fda.gov/news-events/press-announcements/fda-issues-emergency-use-authorization-generic-drug-prevent-new-world-screwworm-cattle?utm_medium=email&utm_source=govdelivery
2. Confirmed Detections of New World Screwworm. USDA. Accessed August 27, 2026. https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/stop-screwworm/current-status/confirmed
3. Freedom of Information summary: original emergency use authorization (EUA) EUA 006729. Bimectin (ivermectin) injectable solution. US Food and Drug Administration. August 27, 2026. Accessed August 27, 2026. https://www.fda.gov/media/194435/download?attachment