The U.S. Food and Drug Administration (FDA) Wednesday announced a voluntary plan to phase out the use of "medically important" antibiotics that make food- producing animals grow faster or more efficiently.

Certain antimicrobials have historically been used in the feed or drinking water of cattle, poultry, hogs, and other food animals for production purposes such as using less food to gain weight. Because some of them are important for the treatment of human infection, there are concerns that this practice may contribute to the development of antimicrobial resistance, which means a drug may no longer be as effective in treating illnesses or infections.

"We need to be selective about the drugs we use in animals and when we use them," William Flynn, deputy director for science policy at FDA's Center for Veterinary Medicine, said in a statement. "Antimicrobial resistance may not be completely preventable, but we need to do what we can to slow it down."

In a final guidance issued Wednesday, the FDA urged animal pharmaceutical companies to voluntarily remove growth enhancement and feed efficiency indications from the approved uses of their medically important antimicrobial drug products, and move the therapeutic uses of these products from over-the-counter (OTC) availability to marketing status requiring veterinary oversight.

Once manufacturers voluntarily make these changes, the affected products can then only be used in food-producing animals to treat, prevent or control disease under the order of or by prescription from a licensed veterinarian, the FDA said.

The FDA said it will ask animal pharmaceutical companies to notify the agency of their intent to sign on to the strategy within the next three months. These companies would then have a three-year transition process.

"This action promotes the judicious use of important antimicrobials, which protects public health and, at the same time, ensures that sick and at-risk animals receive the therapy they need," said Bernadette Dunham, director of the FDA's Center for Veterinary Medicine. "We realize that these steps represent changes for veterinarians and animal producers, and we have been working -- and will continue to work -- to make this transition as seamless as possible." Endi