There are many culprits in the growing problem of microbial resistance to antibiotics—which renders these valuable drugs ineffective—but public health advocates often point to agriculture. Farmers administer more than 70% of the antibiotics used in the United States to improve health and promote the growth of livestock and poultry. Yesterday, the U.S. Food and Drug Administration (FDA) announced changes in farm use of antibiotics designed to safeguard the drugs for medical use.

The American Society for Microbiology applauded the move in an e-mail, calling it "a major step to address antibiotic resistance comprehensively." But critics worry about what they see as a large loophole, and they say the steps don’t go far enough.

Farm animals are often given a constant dose of antibiotics, added to their feed, in order to boost growth and prevent outbreaks of disease. Unfortunately, the practice raises the risk of microbes evolving resistance and eventually spreading to humans. In final guidance released on 11 December, FDA is asking companies that produce drugs for animals to voluntarily change their labels. No longer should they advertise improved growth and feed efficiency from antibacterial drugs that FDA considers medically important to humans.

If the labels change, then the drugs would not be available over the counter. Instead, farmers or feed mills would require a prescription from a veterinarian, who could approve use for treating sick animals or preventing disease in those considered “at risk.” FDA wants to hear from companies within 3 months about their plans to change labels and will give them 3 years to put them in place. The agency preferred a voluntary approach because it says regulatory action would take longer, cost more, and be more disruptive to industry. Companies are supporting the plan.

The Johns Hopkins Center for a Livable Future (CLF), which recently released a report critical of the use of antibiotics in agriculture, is skeptical that the voluntary action will be enough to protect public health. “[T]he guidelines will likely fail to change how these drugs are used in food animals,” according to a statement released today. “The FDA may care whether companies call it growth promotion or disease prevention, but the bacteria do not,” said Keeve Nachman, an environmental health scientist with the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, in the statement. “If antibiotics are used in the same ways, they will have the same effects.”

Christine Hoang, assistant director for scientific affairs at the American Veterinary Medical Association, expects that the change will lead to less use of antibiotics overall. FDA guidance spells out when the drugs should be employed for medical use, she notes, such as providing antibiotics to piglets that are being shipped to a facility with a disease circulating. “All veterinarians know you can’t deviate from the label,” she tells ScienceInsider. “You could lose your license.” Nearly all states require a prescribing vet to be familiar with the keeping and care of animals by a client, even if they don’t require a visit for each prescription.

CLF wants FDA to eliminate all uses of antibiotics for disease prevention. Hoang, however, says that such a ban could pose a “very serious problem for food safety.” If animals get sick, she says, disease can toughen their gastrointestinal tissue, which increases the chance of fecal contamination during slaughter, potentially adding to the spread of resistant microbes. Healthy animals are important for food safety, Hoang says.

Representative Louise Slaughter (D-NY) a longtime proponent in Congress of stricter restrictions on antibiotics in agriculture, said in a statement that FDA is falling short. “The FDA’s voluntary guidance is an inadequate response to the overuse of antibiotics on the farm with no mechanism for enforcement and no metric for success,” she wrote. “Sadly, this guidance is the biggest step the FDA has taken in a generation to combat the overuse of antibiotics in corporate agriculture, and it falls woefully short of what is needed to address a public health crisis.”