The Food and Drug Administration is allowing the use of animal antibiotics that it knows pose a health risk to humans, according to a study released this week.
"The FDA is supposed to protect public health, but they are falling short," said Carmen Cordova, a microbiologist for the Natural Resources Defense Council and the study's lead author.
The NRDC looked at records from 2001 to 2010 (secured through the Freedom of Information Act) and found that the FDA's internal scientific reviews of 30 drugs used in livestock concluded that the drugs likely exposed humans to antibiotic-resistant bacteria through the food supply, the study says.
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At least nine of the 30 antibiotics potentially harmful to humans are still being used in animals, according to the council.
"That's a breach of their responsibility and to the public trust," Cordova argued.
While not responding directly to the NRDC's contention that drugs harmful to humans are being used in animals, the FDA defended its research methods for antibiotic use in livestock.
In a response to CNBC, the FDA said that based on its "review of this [safety data on antibiotics from producers] and other information, the agency chose to employ a strategy that would more broadly address the concerns about the production use of medically important antimicrobials in food-producing animals."
It added that "our strategy also does not limit our authority to take future regulatory action."
U.S. livestock have been given antibiotics for more than 60 years. In fact, 80 percent of the antibiotics used in the U.S. go to livestock.
The FDA approved such use in the 1950s, after studies showed that animals receiving antibiotics in their feed gained weight faster than those that didn't get them. That helped cut farmers' production costs.
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In the 1970s, a study found that overusing antibiotics in animals contributed to the creation of drug-resistant bacteria in humans. The FDA issued a ban on nonmedical use of penicillin and tetracycline in animals but has never fully enforced it.
Though the agency has initiated new rules aimed at limiting antibiotic use in animals for production growth, they are voluntary and involve drugmakers' removing such labels.
Some see widespread use of antibiotics in livestock as a preventative health measure.
"The use of growth promotion is being phased out, but keeping animals from getting sick is judicious," said Kelli Ludlum, director of congressional relations for the American Farm Bureau Foundation, an agriculture advocacy group.