The U.S. Food and Drug Administration has done shockingly little to address the human health risks associated with the overuse of antibiotics in livestock feed, a federal judge said Tuesday, the second time this year a court has told the agency to take action to prevent the abuse of antibiotics in animals intended for human consumption.

Less than three months after a federal court ordered the FDA to begin proceedings to withdraw approval for the non-therapeutic use of penicillin and tetracyclines in animal feed, Judge Theodore Katz ordered the agency to re-examine two citizens petitions asking it to halt the unnecessary use of medically important antibiotics on livestock feed.

Last November, the FDA rejected both of the petitions -- filed in 1999 and 2005 -- without explanation, after staying mum on the issue for years.

For over 30 years, the agency has been confronted with evidence of the human health risks associated with the widespread subtherapeutic use of antibiotics in food-producing animals, and, despite a statutory mandate to ensure the safety of animal drugs, the agency has done shockingly little to address these risks, Katz wrote in his opinion. The court simply finds that the agency's proffered grounds for denying the petitions were arbitrary and capricious.

The FDA did not immediately respond to a request for comment on the ruling. Last month it filed a notice of appeal protesting the March order.

Just over a year ago, a coalition of public health and environmental groups -- including the Natural Resources Defense Council, Center for Science and Public Interest, Food Animal Concerns Trust and Union of Concerned Scientists -- sued the FDA for its inaction regarding the use of growth-promoting antibiotics on animal agriculture.

In 1977, the FDA determined the unnecessary use of huge quantities of antibiotics in livestock feed was connected with a rise in potentially fatal antibiotic-resistant superbugs, leading it to issue petitions calling for the withdrawal of penicillin and tetracyclines in said feed. For more than 30 years, no action was taken -- until days before Christmas 2011, when the FDA surreptitiously withdrew those petitions via an obscure posting in the Federal Register.

In their lawsuit, the coalition of advocacy groups made two key claims: that the FDA failed to fulfill its regulatory responsibility to monitor and withdraw drugs it knew to be potentially hazardous, as evidenced by the 1977 petitions, and that the agency failed to fulfill its responsibility to respond to citizen petitions that essentially asked the FDA to follow its own guidelines.

In March, Katz ruled in the favor of the advocacy groups on the first claim, ordering the FDA to begin proceedings to withdraw approval for those drugs. Previously, the agency said it would focus on encouraging voluntary reform within the agricultural industry instead of  actually enforcing regulatory action. The move was derided by critics, who pointed out the industry has already had more than three decades to voluntarily change its ways.

In his opinion, Katz said the FDA's plan to promote voluntary reform does not excuse the agency from its duty to review the citizens petitions on their merits. The agency must evaluate the safety risks of the petitioned drugs and either make a finding that the drugs are not shown to be safe or provide a reasoned explanation as to why the agency is refusing to make such a finding.

While the FDA has argued that enforcing the regulatory process would be too time-consuming, Katz shot back, calling the excuse both ironic and arbitrary since the withdrawal proceedings could have been commenced and completed if the agency had acknowledged the citizens petitions in a timely fashion.

Scientific literature dating from the 1960s has connected the emergence of sometimes-fatal antibiotic-resistant bacteria with the overuse of antibiotics in livestock feed. Large-scale farmers typically administer livestock feed with small doses of antibiotics, not to treat sick animals, but to ward off bacteria -- often the result of unsanitary living conditions -- that animals would typically expend energy to fight off. The process allows animals such as cows, chickens and pigs to fatten up faster and more efficiently.

Long-term exposure can cause some animals to develop a resistance to antibiotics intended to fight dangerous bacteria, a resistance that can be spread to humans who consume their meat.

In 2009, the FDA itself reported that about 70 percent of all antibacterial drugs in the United States were sold for use in livestock animals to promote growth, prevent disease and treat illnesses caused by unsanitary conditions.