WEDNESDAY, Jan. 4 (HealthDay News) -- Worried about the growing threat of antibiotic-resistant microbes in humans, the U.S. Food and Drug Administration on Wednesday curbed the use of certain antibiotics in cattle, pigs and poultry.

Widespread use of antibiotics in food-producing animals is thought to be a major source of antibiotic-resistant strains of bacteria, experts say.

The new ban includes antibiotics known as cephalosporins, and would take effect April 5, the FDA said in a statement.

The proposed rules, which apply to cattle, swine, chickens and turkeys, are intended to reduce the risk of cephalosporin resistance in certain types of bacteria so that the drugs remain effective in treating disease in humans.

The agency's move "will help to prevent the development of bacterial resistance to this class of drugs," said one expert, Dr. Pascal James Imperato, dean of the SUNY Downstate School of Public Health in New York City.

Another specialist in infectious disease agreed.

"If you use them, you lose them. Antibiotics that is," said Dr. Bruce Hirsch, an attending physician in infectious diseases at North Shore University Hospital in Manhasset, N.Y. "Bacteria are capable of reproducing every 20 to 30 minutes. Antibiotics -- particularly in the low doses used in animals -- exert a selection pressure [on bacteria] which results in antibiotic resistance."

Cephalosporins are used in humans to treat pneumonia, skin and soft tissue infections, pelvic inflammatory disease, diabetic foot infections and urinary tract infections.

If the drugs lose their effectiveness to treat these conditions, doctors may have to use less effective drugs or ones with greater side effects, the FDA explained.

"We believe this [move] is an imperative step in preserving the effectiveness of this class of important antimicrobials that takes into account the need to protect the health of both humans and animals," Michael R. Taylor, Deputy Commissioner for Foods, said in an FDA news release.

Under the new FDA order, prohibited (extra-label) uses of cephalosporins in cattle, swine, chickens and turkeys include:

• unapproved dose levels, frequencies, durations, or routes of administration.
• using cephalosporins that are not approved for use in those species but may be approved for humans or pets.
• administering the drugs for disease prevention.

The order does not limit the use of cephapirin (Cefadyl), an older cephalosporin drug that's not believed to contribute significantly to antimicrobial resistance. Veterinarians will still be allowed to use or prescribe cephalosporins for limited extra-label use in cattle, swine, chickens or turkeys as long as they follow dose, frequency, duration and route of administration instructions on the label.

Extra-label use of the drugs will also be allowed in minor species of food-producing animals, such as rabbits or ducks.

"Cephalosporins are a widely used class of antibiotics that are vital in the treatment of a variety of human infections," Imperato noted. "Their widespread use in food-producing animals is usually undertaken in the interests of preventing certain infections in these animals. These infections in turn can delay animal growth as energy is expended fighting them off.

"However," he added, "the use of these antibiotics in animals also leads to the emergence of antibiotic resistant strains of bacteria. Thus, the FDA decision is a very wise one that will help to prevent the emergence of bacterial resistance and thus assure that this class of antibiotics will continue to be effective for treating human infections."

A comment period on the new order of prohibition begins Jan. 6 and closes March 6. Comments submitted during that time will be considered before the new rules take effect April 5.

More information

The World Health Organization has more about antimicrobial resistance.