Antimicrobial oversight could increase through VFDs

Published on October 26, 2011
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Veterinary oversight could become required for some antimicrobials currently available over the counter to livestock owners.

Federal drug authorities also plan to increase restrictions on extralabel use of cephalosporin-class antimicrobials.

Dr. William T. Flynn, deputy director for science policy in the Food and Drug Administration, said the agency could begin requiring veterinary feed directives for many of the antimicrobials currently available for use in animal feed without prescriptions. He said the agency is considering changes to the regulations governing the directives, which allow administration of medicated feeds under the supervision and direction of a veterinarian.

"The concern was the existing (VFD) process (is) just simply too onerous, and it was going to create some really significant workability issues if we go in this direction," Dr. Flynn said. "That's something we've identified and have been trying to get input on, is how to improve that process."

Dr. Flynn made the comments during a session on antimicrobial resistance at the American Association of Bovine Practitioners annual conference Sept. 22-24 in St. Louis. He said the FDA is considering ways to phase out nontherapeutic use of some antimicrobials important for use in human medicine while ensuring the drugs remain available for treatment of animal disease. The agency is most concerned about products approved before 2003, when the FDA began considering the potential risk posed by antimicrobial resistance in the drug approval process.

Dr. M. Gatz Riddell, executive vice president of the AABP, said his organization favors increased veterinary oversight of antimicrobial use and has given the FDA comments on ways to streamline the VFD process. He expects the FDA to consider requiring VFDs for nearly all antimicrobials currently available over the counter for use in the feed of food animals. Ionophores are likely among the few exceptions, although bambermycins could also be exempt from VFD-related requirements, he said.

Dr. Flynn similarly said that his agency's concerns regarding antimicrobial resistance applied only to drugs relevant to human medicine and not to those with no counterparts or limited uses in human medicine.

Dr. Riddell said some cattle veterinarians have expressed concerns that, because no products for use in cattle have been labeled as VFD drugs, their unfamiliarity with the VFD process could lead to confusion and errors. He hopes to partner with the agency, however, to provide training for cattle veterinarians.

The workload required to issue sufficient VFDs for large herds is a concern, Dr. Riddell said. He estimated that if a veterinarian needs to write VFDs for individual pens on a feedlot with about 100,000 cattle, that veterinarian could write about 2,200 VFDs annually. Instead, the AABP would prefer that a veterinarian be allowed to write directives that would apply over 6 to 12 months to animals managed in identical conditions and needing identical preventive measures.

Dr. Flynn also said the FDA plans to issue in the near future an order that would increase restrictions on the use of cephalosporin-class antimicrobials in food animals. In July 2008, the FDA issued an order that would have, by October 2008, banned all extralabel use of such drugs in food-producing animals. The agency extended the comment period and subsequently revoked the order, citing the need to fully consider comments. FDA officials had indicated a revised version of the cephalosporin extralabel use ban would be published, at one time indicating the new order was expected in summer 2009.

The AVMA was among veterinary organizations that opposed the 2008 order, stating in comments to the agency that the restrictions could have unintended negative consequences for animal health and welfare and decrease food safety without providing the desired improvements to human health. The Association requested that the FDA delay the order and further assess the risks and benefits.

Dr. Riddell said the AABP has not seen evidence connecting antimicrobial resistance among foodborne pathogens to extralabel cephalosporin use, as opposed to use according to the label. He said the AABP wants a rigorous system that could determine whether a drug's use is connected with resistance and whether restrictions on extralabel use of a drug are connected with changes in resistance.

The FDA's Federal Register notice for the 2008 order states that reduced susceptibility to veterinary-use ceftiofur was connected with reduced susceptibility to human-use ceftriaxone, both of which are cephalosporin-class antimicrobials. The agency acknowledged in that order that few data were available to show the extent of extralabel veterinary cephalosporin use, but inspections of eight poultry hatcheries in 2001 and examination of the facility records indicated that ceftiofur was used in an extralabel manner in six of the facilities.

"For example, ceftiofur was being administered at unapproved dosing levels or by unapproved methods of administration," the 2008 order states. "In particular, ceftiofur was being administered by egg injection, rather than by the approved method of administering the drug to day-old chicks."

Some cephalosporin antimicrobials are currently approved for use in dairy cattle to treat bovine respiratory disease, foot rot, shipping fever, pneumonia, pododermatitis, uterine infection, and mastitis. Extralabel uses have included treatment of septicemia and peritonitis, as well as use as a post-operative prophylactic antimicrobial.

Cephalosporin antimicrobials are also labeled for use in poultry to control Escherichia coli and early mortality. Extralabel uses have included prophylaxis for young birds and eggs at high risk of bacterial infection.