FDA Finalizes Guidance on Duration Limits for Medically Important Antimicrobials in Livestock

On February 13, 2026, the U.S. Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM) published a Final Guidance titled “Defining Durations of Use for Approved Medically Important Antimicrobial Drugs Fed to Food-Producing Animals” (GFI #273). The Final Guidance provides updated recommendations for sponsors of medically important antimicrobials administered in feed that have at least one approved indication with an undefined duration of use[1] (“Affected Products”) to define duration of use in product labeling. CVM’s issuance of the Final Guidance reflects FDA’s ongoing effort to combat the incidence of drug-resistant microbes by promoting the judicious use of medically important antimicrobials in the feed of food-producing animals.

CVM’s stated objective in issuing the 2023 Draft Guidance and the Final Guidance is to provide recommendations to sponsors on how to revise the product use conditions (e.g., dosage regimen, instructions for use) for Affected Products “to better target when and for how long a drug may be used to effectively treat, control, or prevent the disease(s) for which the product is indicated.” The Draft Guidance established a voluntary framework for such labeling changes, focused on defining the appropriate duration of use in animals within the drug’s maximum permitted duration of use. The Final Guidance generally adopts the same framework, but provides revised recommendations on how an appropriate duration of use should be established among other changes.

Key Changes in the Final Guidance:

Appropriate Duration of Use: The 2023 Draft Guidance defined an “appropriately defined duration of use” as when “the information regarding duration of feeding on the labeling ensures that the drug is used only when animals need it and provides the veterinarian appropriate flexibility to use the drug consistent with the labeling in a range of scenarios that may be encountered in practice.” The Draft Guidance stated that an appropriately defined duration of use “should consist of an expected duration bounded by a maximum permitted duration.” The Final Guidance changes the suggested approach from an “expected” duration of use to a “typical” duration of use, explaining that an appropriately defined duration of use should describe the approximate duration range that veterinarians should first consider for the indication (i.e., the typical duration range), which should be bounded by a maximum permitted duration. The Final Guidance suggests an intent to provide greater flexibility for veterinarians to use their medical judgement to define an appropriate duration of use on a case-by-case basis, stating that “[v]eterinarians ultimately may authorize, in accordance with their professional judgement in varying clinical circumstances, a duration that falls outside of the typical duration range up to the maximum permitted duration described on the labeling.” It also provides that in the case of treatment or control indications, the labeling directions for use should be defined in terms of evidence of disease in the animal group, while for prevention and prevention-like indications, duration of use should be defined as the period during which animals are at risk for the disease.

Timelines for Labeling Changes: Like the Draft Guidance, the Final Guidance advises sponsors to submit proposals for labeling changes for Affected Products, via supplemental applications, and provides instructions and timelines for submission and CVM review. While the Draft Guidance instructed sponsors of top-level NADAs[2] that serve as references for one or more downstream applications or files to submit such supplements no later than 3 months following finalization of the guidance, the Final Guidance states that such submissions should be made no later than 6 months after finalization. Sponsors of top-level NADAs that do not serve as references for any downstream applications or files should submit no later than 1 year after finalization, as noted in the Draft Guidance. In addition, while the Draft Guidance advised that such supplements should include duration of use statements such as “continue [for at least X days] or [until the animals no longer require this medication]” based on disease evidence or risk, the Final Guidance proposes different language, such as “continue for approximately A to B days,” and emphasizes use of the statement “Do not feed for more than X days.”

Establishing Duration of Use: The Final Guidance further explains the justification a sponsor should provide (before submitting its labeling supplement) to CVM to establish a proposed duration of use, including the proposed typical duration range and the maximum duration of use for each indication. Sponsors should base their justifications on typical and potential disease risk periods, observed disease progress, self-cure timeframes, usual and maximum timeframes to expected outcomes, and other relevant information as applicable. As noted in the Draft Guidance, sponsors should comprehensively support the proposal with a scientific justification based on relevant available evidence such as peer-reviewed scientific literature, recognized standards of veterinary practice, a consensus of expert opinions, and other such information. The sponsor may also rely upon existing information relevant to the drug, including studies in the application file that were used to support approval and information related to mechanism of action, pharmacokinetics, and pharmacodynamics.

Additional Recommendations: The Draft Guidance advised sponsors to include an “Additional Recommendations” section in Affected Product labeling, explaining that the maximum permitted duration of use should not be routinely ordered, as well as information for each indication, as appropriate, to assist the veterinarian in determining when drug feeding should be initiated or stopped in accordance with the approved conditions of use. This information is intended to assist the veterinarian when writing a VFD. The Final Guidance additionally instructs that this section should state that veterinarians should first consider prescribing within the typical duration range.

If you have any questions concerning the material discussed in this client alert, please contact the members of our Animal Food and Drug practice.