OMAHA (DTN) -- The Food and Drug Administration's latest move to limit extra-label use of a certain class of antibiotics gives veterinarians leeway to prescribe the drug for off-label purposes as long they comply with the label's dosing instructions.

FDA released a rule in 2008 that banned all extra-label, or non-FDA-approved, uses of the cephalosporin class of drugs but retracted it after the livestock industry expressed concerns that the rule was too broad. In the revised order released Wednesday, FDA stated that only two of the comments about the 2008 rule supported that rule as written.

"That was a very broad, sweeping prohibition and it disallowed veterinarians from really having any leeway in the practice of the medicine," said Christine Hoang, assistant director of the scientific activities division of the American Veterinary Medical Association. "This is a much narrower, targeted order of prohibition and allows more flexibility for the veterinarian to be able to treat animals."

FDA is concerned that rising levels of bacteria resistant to cephalosporins could lessen those antibiotics’ effectiveness in humans. There are many different drugs within the cephalosporin class, and resistance to one drug makes others in that class less effective. Such cross resistance could render one of human medicine's big guns ineffective.

The FDA noted that a salmonella monitoring program was established in the late 90s because food animals were a known source of resistant salmonella infections in humans. The program's research showed none of salmonella bacteria collected from cattle in 1997 showed resistance to ceftiofur, a drug within the cephalosporin class. In 2009, 14.5% of the samples were positive for resistance. The program monitored resistance in humans and found resistant bacteria populations increased there too, although not as steeply. Cephalosporin drugs are important in the treatment of salmonella, pneumonia and many other bacterial infections in humans.

In cattle, cephalosporin drugs are used extensively to treat pneumonia, said Dr. M. Gatz Riddell, executive vice president of the American Association of Bovine Practitioners. Veterinarians also use cephalosporins to treat foot rot and uterine infections. All of those conditions are approved uses and aren't affected by FDA's prohibition order.

The new order only changes rules regarding extra-label use. The order excludes cephapirin, an older drug in the class that's not linked to increased bacteria resistance. It's often used to treat bovine mastitis and can be found in some over-the-counter medicines.

Riddell said cephalosporin drugs are often used to treat relatively rare infections, such as an infection of the pericardial sac surrounding cattle's hearts. The infrequency of those infections makes it unaffordable for pharmaceutical companies to do the laboratory testing required to get FDA's approval to make it an on-label use.

"You can't change the dose or duration or route of administration, but the one thing FDA did allow in this prohibition, which we frankly are very gratified to see, is that they allowed veterinarians to look at a sick animal and make a diagnosis, possibly of one of these very infrequent cases, and with their knowledge of microbiology and pharmacology decide that cephalosporin at the label dose would be an appropriate antibiotic to use," Riddell said.

The order bans use of cephalosporin drugs to prevent disease. Cephalosporins are not mixed with feed and their use for disease prevention was relatively slim. A vet might administer a cephalosporin before surgery if he believed there's a high risk of infection, Hoang said. Vets won't be able to do so after April 5 when the ban goes into effect. FDA will publish the order in the Federal Register on Friday and will accept comments on the updated rule for 60 days.

Antibiotic resistance and the transmission from farm animals to humans is extremely complicated, Riddell said. "You can take two highly trained epidemiologists and they can look at the same information and come up with two very drastically different conclusions based upon what variable they plug into their calculations and evaluations.

"They're (FDA) under intense pressure from the human side, so if they can restrict some uses it might be seen as a good thing," he said.

Katie Micik can be reached at katie.micik@telventdtn.com

(AG)

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