This year’s report shows that domestic sales and distribution of medically important antimicrobial drugs approved for use in food-producing animals decreased by 3% between 2019 and 2020. That is a 38% decrease since 2015, which was the peak year of sales. This suggests that continued efforts to support the judicious use of antimicrobials in food-producing animals are having an impact, the FDA said in a press release.

Sales data on antimicrobial drug products intended for food-producing animals do not necessarily reflect the actual use of antimicrobial drugs. However, sales volume observed over time can be used as an indicator of market trends related to these products. FDA warns, though, that it is important to take into account additional information sources including actual use data, animal demographics, animal health data, and data on antimicrobial resistance when evaluating the progress.

FDA's goal is to slow the development of antimicrobial resistance and preserve the effectiveness of antimicrobials for fighting disease in animals and humans. The agency’s aim is not simply measured by a reduction in sales volume of antimicrobials, but also includes fostering good antimicrobial stewardship practices by optimizing the use of these products and limiting their use in animals to only when necessary to treat, control, or prevent disease.

FDA recognizes that fluctuations in sales volume may occur over time in response to various factors, including changing animal health needs or changes in animal populations. Given the substantial change that occurred with transitioning a large number of products containing medically important antimicrobials from over-the-counter use to a marketing status requiring veterinary oversight at the beginning of 2017, some rebound in the reported sales volume in subsequent years was not unexpected as affected stakeholders adjusted to the new requirements.

When analysing the report, one should consider sales and distribution information does not represent actual use of the products.

It is important to acknowledge that these data represent sponsor estimates of product sales and are not intended to be a substitute for actual usage data. For example, veterinarians and animal producers may purchase drugs, but never actually administer them to animals, or they may administer the drugs in later years.

Before making a direct comparison between the quantity of antimicrobial drugs sold for use in humans and that sold for use in animals, you should consider that there are many more animals than humans. For instance, there are approximately 331 million people in the US, while USDA records indicate that about 9.3 billion chickens are slaughtered annually.

One should also consider that there are differences in physiology and weight between humans and animals, said FDA. The average adult human weighs 185 lbs., while the average live weight for a beef cattle is about 1,373 lbs.

Different animal species metabolise drugs differently, meaning that some species may require more of the drug to be effective, or may need to be treated for a longer period of time.

The agency cautions against making direct comparisons of species-specific sales estimates. There are a variety of factors that confound direct comparison of species-specific sales estimates, including differences in the population size, weight, lifespan, and drug metabolism of each species.

The agency also cautions against making direct comparisons between the sales volume of different drug classes. Direct comparison of sales volumes for different drug classes is problematic because not all drug classes are approved for use in all species, not all drug potencies are the same, and not all of the drug classes can be used interchangeably to treat the same conditions.

While there has been progress made toward antimicrobial stewardship goals, additional work is needed to address antimicrobial resistance. The Center for Veterinary Medicine’s five-year action plan outlines steps the Agency is pursuing to further foster antimicrobial stewardship in veterinary settings.