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Volume and Rate of Antibiotic Use in Animals and Humans

Inconsistent data collection makes comparisons difficult

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Experts agree that we need to use antibiotics responsibly in both humans and animals to help curb antibiotic resistance, yet it’s also important to understand the differences between human and animal antibiotics.

While both human and animal antibiotics are prescribed by medical professionals, the prescribing doctors and veterinarians administer them differently. Humans receive individual therapies for their specific ailment. While individual animals can be treated with specific antibiotics, it is most common for antibiotics to be administered to groups via the feed or water.

While it is tempting to compare volume of antibiotic use between animals and humans, it is hard to draw firm conclusions from these comparisons because data collection practices are rudimentary, the categories of antibiotics used in animals and livestock are not identical, and the size of the populations (animals vs. humans) are hugely imbalanced.

Furthermore, while some antibiotics are used in both people and animals, a large portion of antibiotics that are FDA-approved for use in animals are not used in human medicine and therefore do are not a threat to create resistance in humans. For example, of the antibiotics used in farm animals today, about one-third are a category called ionophores. Ionophores are not medically important to humans and are not used in human medicine. This means that ionophores cannot contribute to resistance in antibiotics important in human medicine.

Understanding the Data

There is currently no solid data on antibiotic use in human medicine – commonly used figures are extrapolated from data about antibiotic sales that FDA purchases from private vendors. The FDA has specifically said that human sales numbers and usage numbers are not to be compared to livestock usage numbers. Furthermore, many believe more data is needed to better understand the uses of antibiotics in agriculture. The agriculture community is supporting efforts to fund programs at USDA that will facilitate this understanding and help farmers become better users of antibiotics.

Different Classes of Antibiotics

Human medicine relies heavily on the penicillin class. The amount of penicillins sold is more than twice as much for millions of people as they are for billions of animals.

• Veterinary medicine relies more on tetracyclines, which comprise about 60% of all medically important antibiotics sold for food animals.

• Other than tetracyclines and ionophores, the percent of each antibiotic class sold for human use is greater than for animal use.

• About 31 percent of the total amount of antibiotics used in food animals are ionophores – compounds not used in human medicine and thus not contributing to the burden of antibiotic resistance in humans.

• Compounds more important in human medicine – including fluoroquinolones and 4th generation cephalosporins – are used sparingly in animals, about 1% or less of all antibiotics sold.

The more difference there is between antibiotics used in humans and those used in animals, the more we can reduce the potential for animal use impacting humans.

Understanding the Numbers

It is true that more antibiotics are used in animals than humans, but there are far more animals in the U.S. than people. There are more than 90 million cattle, 5.3 million sheep and lamb, 66 million hogs, 200 million turkeys and eight billion chickens on U.S. farms. The combined weight of livestock and poultry in the U.S. is roughly 3.5 times that of the combined weight of American men and women. A 1,200 pound steer is equal to roughly six men. If a steer needs treatment for pneumonia, logic will tell you that it will require a larger dose than a person. Similarly, it is logical that our combined U.S. livestock and poultry herds and flocks will require more antibiotics by volume than our combined human population.