Antibiotic Stewardship in Animal Agriculture Requires Defined Durations of Use

The U.S. Food and Drug Administration (FDA) implemented a federal policy in January 2017 making it illegal to use medically important antibiotics to promote animal growth and requiring veterinary oversight to add them to feed and water. This marked a milestone in ensuring that antibiotics are used judiciously on farms, which is essential to slow the emergence of resistant bacteria.

However, many medically important antibiotics can still be used legally in ways that do not meet FDA’s own definition of judicious use. For example, some antibiotic labels allow for very long or undefined durations of use, are approved for non-specific conditions such as to “maintain weight gains during times of stress,” or permit overly broad dosage ranges. FDA should act to address these problematic uses as soon as possible and ensure that all uses of these drugs in animals are under veterinary oversight and align with judicious use principles.

Q: What are “duration limits” and why are they important?

A: Duration limits specify the appropriate length of time for which a drug should be used to address a given indication. Establishing a science-based duration limit is a central part of FDA’s current animal drug approval process, but many animal antibiotics were approved before these requirements were in place. Using the right antibiotic for the appropriate amount of time is fundamental to antibiotic stewardship. FDA has stated that “long-term or open-ended use of medically important antibiotics is a significant stewardship issue,” and that “medically important antibiotics labeled for continuous or undefined durations of use is not consistent with judicious use.” Giving veterinarians well-defined duration limits based on scientific data is an important part of combating antibiotic-resistant bacteria because all use of antibiotics in human or animal medicine promotes the emergence of resistance that threatens the drug’s effectiveness. Appropriate durations of use also protect the health of food animals, and they help veterinarians ensure that these drugs are administered for an amount of time most likely to yield the desired clinical response.

Q: How many antibiotics approved for use in animals lack duration limits?

A: Almost 30 percent of the labels have open-ended or undefined durations of use. Among those with limits, some far exceed two or three weeks. And others have duration limits that are tied to subjective or poorly defined external factors, such as when the animal experiences “times of stress.”

Q: What effect would duration limits have on animal health and veterinary care?

A: Ensuring that all animal antibiotics have science-based duration limits would not undermine a veterinarian’s ability to prescribe antibiotics to protect an animal’s health. Rather, duration limits—when based on robust scientific evidence—help the veterinarian administer the antibiotic for the right amount of time and guide the veterinarian’s decision-making.  

If an antibiotic is administered for an improper amount of time, it can endanger human and animal health. The emergence of antibiotic resistance can further limit already restricted treatment options for food animals and potentially compromise a veterinarian’s ability to effectively treat a sick animal. 

It is also important to note that other tools—such as good management practices and nonantibiotic alternatives—can significantly reduce the need for antibiotics and that use of these strategies is a fundamental part of antibiotic stewardship.   

Q: Will establishing duration limits for animal antibiotics be difficult?

A: Many antibiotics for use in animals already have duration limits, and for the remaining drugs that still lack them, drug sponsors could easily reference comparable antibiotics already approved for identical or similar indications that have well-defined duration limits.  

Q: Has FDA recognized this issue?

A: In July, FDA Commissioner Scott Gottlieb announced that duration limits will be addressed as a part of the agency’s five-year plan to advance antimicrobial stewardship in veterinary settings. He committed to keeping an up-to-date list of all medically important antibiotics lacking duration limits. Previously, in September 2016, FDA requested public comments on how to establish appropriate duration limits. Specifically, the agency requested input from stakeholders on the best approach for updating the problematic labels, how antibiotics without duration limits are used on farms, what factors influence veterinarians’ determinations about when to use these antibiotics, and which alternative products are available to manage animal health. These are important issues and FDA should take action now to address duration limits to ensure that antibiotics are used judiciously in animal agriculture.