* Judge critical of FDA's lack of action

* Long-standing concerns about creation of superbugs

* FDA unveiled voluntary guidelines in April (Rewrites with quotes from judge and industry group comments)

By P.J. Huffstutter

June 5 (Reuters) - A federal judge said the Food and Drug Administration had done "shockingly little" to address the human health risks of antibiotic use in animal feed and ordered the agency to reconsider two petitions seeking restrictions on the practice.

The ruling, filed on Friday in a lawsuit brought by environmental and public-health groups, is the second recent setback for the FDA amid long-standing concern that overuse of antibiotics in animal feed is endangering human health by creating antibiotic-resistant bacteria.

U.S. Magistrate Judge Theodore Katz in New York questioned the federal agency's arguments that it would be less costly and more efficient to ask the industry to voluntarily cut back on the use of such antibiotics, rather than go through the regulatory process of revoking the approval of such drug use on farms and at feed lots.

"For over thirty 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 March, Katz ordered the FDA to complete proceedings to withdraw approval for the non therapeutic use of penicillin and tetracycline in livestock production unless makers of the drugs can produce evidence that their use is safe. The agency started the process in 1977, but never completed it.

The FDA declined on Tuesday to comment on the latest ruling. It filed a notice of appeal last month of the March order.

In his latest ruling, Katz found that the FDA behaved in an "arbitrary and capricious" manner when it dismissed two citizens' petitions that asked the agency to consider banning farmers from using antibiotics on livestock for non-therapeutic uses.

The FDA had rejected the two petitions - filed in 1999 and in 2005 - because of the time and expense to hold formal withdrawal proceedings.

How many livestock farmers use such antibiotics on their animals, and how frequently the drugs are used, is unknown. An estimated 80 percent of all antibiotics sold in the United States are for use in agriculture, according to data reported by the FDA.

YEARS OF CONCERN

As far back as 1972, a federal scientific task force found that the use of low-level doses of antibiotics in animal feed favored the development of antibiotic-resistant bacteria; that such bacteria had been found on meat sold to the public; and that the prevalence of such bacteria in humans had increased.

Katz's latest ruling adds fuel an intensifying legal war over the future use of antibiotics to promote animal growth, increase feed efficiency and disease prevention on food-producing livestock.

The ruling also highlights the potential for future shifts in federal regulations over animal agriculture practices. Such changes could force beef, pork and poultry producers to buy more grain and find other ways to fatten animals prior to slaughter.

Critics of antibiotics in animal feed called the ruling a victory in an increasingly contentious fight.

Organizations such as the Union of Concerned Scientists and the American Academy of Pediatrics argue that such farming practices endangers people who grow ill from resistant bacteria but cannot be treated with standard antibiotic therapies.

"We want them to evaluate safety and effectiveness (of such practices), and we think that's something the FDA has been avoiding," said Avinash Kar, an attorney for the Natural Resources Defense Council. "We think they've caved into the industry."

The livestock industry was disappointed by Katz's order, and said the use of such medications is necessary to prevent and treat animal health issues.

Industry officials, citing conflicting scientific research, say such practices pose little risk to public health.

"The actual human health risk of the use of antibiotic use in animals resulting in the inability of the drug to treat human disease is extremely small - in one instance, less than the risk of dying from a bee sting," the Animal Health Institute, a trade group that represents pharmaceutical companies, said in a statement on Tuesday.

The agency unveiled voluntary guidelines this past April for both drug manufacturers and livestock producers to curtail the use of antibiotics on farm animals.

But Katz said that these voluntary measures are not a substitute for the FDA reviewing the petitions.

"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," Katz wrote.

The lawsuit seeking to spur the FDA to restrict antibiotic use in animals was filed in 2011 by groups including The Natural Resources Defense Council, Center for Science in the Public Interest and the Union of Concerned Scientists.

The case is Natural Resources Defense Council et al. v. FDA, in the U.S. District Court for the Southern District of New York, No. 11-3562. (Reporting by P.J. Huffstutter and Sakthi Prasad; Editing by Tim Dobbyn)