July 2 (Bloomberg) -- Inspectors found a common antibiotic has been misused in animals through practices such as injections into chicken eggs and ordered farm veterinarians to stop the unapproved treatments because of the risk to humans.

The drugs, called cephalosporins, were given in unapproved doses to chickens, beef and dairy cows and pigs, the U.S. Food and Drug Administration said today on its Web site. Cephalosporins are approved to treat respiratory infections in livestock and to treat day-old chicks to prevent infections, the FDA said.

Doctors use cephalosporins on humans to treat skin infections, stomach infections and pneumonia. Widespread treatment of animals with the same drugs increases the risk that food-borne bacteria, among them salmonella and E. coli, will develop resistance.

``If these drug-resistant bacterial strains infect humans, it is likely that cephalosporins will no longer be effective for treating disease in those people,'' the FDA said. ``Given the importance of the cephalosporin class of drugs for treating disease in humans, FDA believes that preserving the effectiveness of such drugs is critical.''

Under FDA rules, veterinarians can prescribe drugs to animals for uses that haven't been approved unless the agency determines that it poses a risk to public health.

Drug-Resistant Salmonella

Researchers examined records from programs set up to monitor drug resistance in animals in the U.S., European Union and Canada. In the U.S., a type of drug-resistant salmonella that didn't exist among cattle in 1997 was found in about 19 percent of salmonella samples taken from animals ready for slaughter in 2006. About the same time, drug resistant salmonella increased to 3.4 percent from about 0.2 percent in samples taken from people.

It's not clear how many U.S. farms were using the drugs in dangerous ways, the FDA said. Six of the eight chicken hatcheries inspected in 2001 were giving unapproved treatments, according to today's report.

The new rules won't affect uses that have been approved or future approvals, FDA spokesman Michael Herndon said in an e- mail. In order to gain clearance for a new drug, companies must submit evidence that it won't increase drug resistance, he said.

To contact the reporter on this story: Tom Randall in New York at trandall6@bloomberg.net.

Last Updated: July 2, 2008 18:59 EDT