(Corrects paragraph nine to clarify how resistance to antibiotics develops in bacteria)
By P.J. Huffstutter
CHICAGO, March 26 (Reuters) - U.S. regulators on Wednesday said that 25 out of 26 drugmakers that sell antibiotics used in livestock feed for growth enhancement have agreed to follow new guidelines that will make it illegal to use their products to create beefier cattle, heftier hogs and other outsized animals.
The companies - which include Eli Lilly & Co's Elanco Animal Health unit, Bayer Healthcare LLC's animal health division and Zoetis Inc - have agreed to start the process of removing any growth promotion claims on their products' labeling, according to the U.S. Food and Drug Administration.
The FDA announced the guidelines in December, as part of an ongoing bid to stem a surge in human resistance to certain antibiotics. Although the guidelines are voluntary, agency officials have said they expect drugmakers to fully adhere and to narrow their products' use.
This labeling shift will ultimately mean that while farmers, ranchers and other agriculture groups can continue to use such drugs to treat sick animals, they will be banned from using them for promoting growth in livestock, according to regulators.
"The FDA and drug makers appear to have passed the first big test of the agency's voluntary approach," said Laura Rogers, director of human health and industrial farming for The Pew Charitable Trusts, adding "there's a lot more to do."
Critics argue that the guidelines give drugmakers too much discretion in policing their own use of antibiotics and provide no mechanism for enforcement, and were unconvinced by Wednesday's announcement.
"This plan is likely to lead to label changes, not a reduction in use," said Avinash Kar, health attorney with the Natural Resources Defense Council.
Public health experts have become worried in recent years about the emergence of new strains of bacteria that cannot be controlled by a wide range of current antibiotics.
Some suspect that these "superbugs" have developed as a result of livestock being fed low-levels of antibiotics throughout much of their lives, creating an environment for bacteria to mutate and develop resistance to drugs that are key to human health.
The companies have also agreed to require such antibiotics, which are typically added to animals' food or water, to be made available only through a veterinary prescription or via a veterinary feed directive status - instead of being available for sale over-the-counter at feed stores and other retail outlets, according to regulators.
On Wednesday, the agency said there are currently 26 drug companies and a total of 283 affected products or applications that fall under the voluntary guidance.
Of the 26, Pharmaq AS was the only company that declined to follow the voluntary guidelines. Pharmaq makes an antimicrobial powder used to treat certain conditions in salmon, trout and catfish. The Norwegian company's product already is for therapeutic uses only, but is available over the counter, according to nutritionists.
The full list of companies can be found on the FDA site here: http://www.fda.gov/AnimalVeterinary/SafetyHealth/AntimicrobialResistance/JudiciousUseofAntimicrobials/ucm390738.htm (Reporting by P.J. Huffstutter, editing by Ros Krasny and Bernard Orr)