The FDA has allowed dozens of antibiotics to be used in animal feed, despite findings that the drugs could expose humans to antibiotic-resistant bacteria, an advocacy group says in a new report. (Carrie Antlfinger/AP)

The Food and Drug Administration has continued to allow dozens of antibiotics to be used in livestock feed, despite findings from its researchers that the drugs could expose humans to antibiotic-resistant bacteria through the food supply, an environmental advocacy group said in a report Monday.

FDA officials reviewed about 30 animal-feed additives between 2001 and 2010, rating 18 of them “high risk” in terms of contributing to health problems in humans, according to records obtained through the Freedom of Information Act by the Natural Resources Defense Council. The remaining drugs the agency examined did not have adequate data to determine whether they were safe, the report said.

According to the NRDC, at least 26 of the feed additives that FDA researchers reviewed — some of which have been in use since the 1950s — did not meet standards set by the agency in 1973 that required companies to submit scientific studies proving that the drugs were safe.

The report comes amid increasing worries in the public health world about the problem of antibiotic-resistant infections, which sicken millions of Americans each year and kill an estimated 23,000. Public health officials across the globe have warned that the misuse and overuse of antibiotics are causing more and more of the drugs to lose their effectiveness, meaning that even routine infections could become untreatable.

Carmen Cordova, an NRDC microbiologist and lead author of the analysis, called the FDA’s failure to act on its own findings “a breach of their responsibility and the public trust.”

Avinash Kar, an NRDC lawyer, said it underscores a larger pattern of FDA inaction in combating the overuse of antibiotics in animals, something scientists and doctors widely believe is contributing to the proliferation of hard-to-treat infections.

“They are not meeting their responsibility to protect public health,” Kar said. “They need to be doing better.”

The penicillin- and tetracycline-based antibiotics at the center of the NRDC’s analysis were approved for “non-therapeutic” or “subtherapeutic” uses, such as bolstering growth in animals.

In a statement Monday, the FDA said the review highlighted in the NRDC report was “part of the agency’s overall effort to assess available, current information regarding antimicrobial resistance concerns associated with the use of medically important antimicrobial drugs in food-producing animals.”

Rather than focus on specific drugs, the agency said, it decided to pursue a broader strategy of trying to phase out non-therapeutic uses of antibiotics over time.

It is unclear how many of the drugs the agency examined continue to be sold by manufacturers. NRDC researchers said they found evidence suggesting that at least nine of the feed additives continue to be marketed; aside from two that companies voluntarily withdrew, all others remain approved for use.

Although the FDA did send letters to some companies seeking more information about concerns that the drugs might promote antibiotic resistance, the documents obtained by the NRDC did not show that the agency took further action or that the companies submitted additional safety studies, the report states.

The vast majority of antibiotics sold each year in the United States — by some estimates as much as 80 percent — are used in agriculture rather than in human medicine. Consumer and environmental groups have pressed lawmakers and regulators to do more to limit the amount of antibiotics given to animals, particularly those classes of drugs also used to treat humans.

Last fall, the Centers for Disease Control and Prevention issued an alarming report detailing the growing threat of antibiotic-resistant infections. Although most such infections arise in hospitals and nursing homes, officials underscored the widespread use of antibiotics in animals as a looming concern.

“Resistant bacteria can contaminate the foods that come from those animals, and people who consume these foods can develop antibiotic-resistant infections,” the CDC report stated. “The use of antibiotics for promoting growth is not necessary, and the practice should be phased out.”

The FDA seems to agree. In 1977, the agency said it planned to withdraw approval for some animal antibiotics, especially those used for nonmedical reasons. But for decades, the agency took no action, even as the NRDC sued in recent years, trying to force it to follow through.

In December, the FDA took long-awaited steps aimed at scaling back the use of antibiotics in livestock. The agency asked animal-drug manufacturers to alter their labels so that farmers would no longer be allowed to use antibiotics merely to promote growth. It also wants farmers to get approval from a veterinarian before administering the drugs to livestock.

The agricultural industry largely welcomed the move, saying it would lead to meaningful changes in how antibiotics are used on farms. Consumer advocates and some public health officials were less than impressed, saying the FDA didn’t go far enough and complaining that its recommendations were voluntary.

The FDA said Monday it remains confident that its current approach, which will give animal-drug companies and the agricultural industry several years to adapt, “is the most efficient and effective way to change the use of these products in animal agriculture.”