The Bayer Corporation is enlisting the veterinary community and food animal industry to help ensure that scientific evidence prevails when the government decides whether to allow continued use of its fluoroquinolone Baytril (enrofloxacin) to treat poultry diseases.
A reported national increase in fluoroquinolone-resistant Campylobacter infections in people in 1999 led the Food and Drug Administration's Center for Veterinary Medicine to ask Bayer in October 2000 to voluntarily withdraw the product.
Bayer disagrees with the FDA-CVM's conclusions about Baytril, which were based, in part, on a review of the data collected in 1999 under the National Antimicrobial Monitoring System. The company contends that Baytril is a vital antimicrobial that eliminates serious bacterial infections in poultry.
In fall 2000 the agency announced its intention to begin the process of withdrawing approval for the drug's new animal drug application, which had been given in 1996.
On Feb. 20, 2002, the FDA-CVM granted the company's request for a hearing. Bayer took the next step March 21 by filing a Notice of Participation. According to Bayer, if the FDA administrative judge accepts the proposed hearing schedule, motions would be submitted beginning April 15, 2002, and final cross-examination of rebuttal witnesses would conclude in December 2003.
The hearing will discuss whether new evidence shows that enrofloxacin is not safe for use under the conditions upon which it was first approved. This includes whether there is a reasonable basis for serious questions about the safety of enrofloxacin use in poultry and whether the use of enrofloxacin under the approved conditions of use in poultry has been shown to be safe.
At the hearing, the company will present new findings in support of Baytril use in poultry. John B. Payne, senior vice president, Bayer Animal Health, said, "We believe we have a compelling case that the use of Baytril in chickens is not a threat to public health, and we look forward to presenting our scientific evidence before the judge."
In a March 21 letter sent to "colleagues in the veterinary sciences and food animal industries," the company asks for help in dispelling myths and raising awareness of the contributions Baytril makes to ensuring a healthy food supply.
According to Bayer, one misconception is that use of Baytril in poultry might reduce the effectiveness of its human fluoroquinolone Cipro in treating anthrax infection. Another fallacy is that Baytril is used for growth promotion and preventive treatment.
The letter states: "We believe that the data do not support CVM's conclusion that a national trend of rising resistance occurred. Furthermore, our analysis of government NARMS data for 2000 confirms that stance."
Baytril may be used only under a veterinarian's supervision. It is currently used in less than 1 percent of chickens, when serious disease threatens flock health.
The AVMA is encouraged that the FDA will hold hearings before a final decision is made to retain or withdraw approval of enrofloxacin to treat poultry diseases. In December 2000, in response to the notice of an opportunity for a hearing, the AVMA submitted an evaluation of the scientific reasoning behind the FDA's action. The Association recommended that a hearing be conducted so that the scientific evidence could be presented. In its evaluation, the AVMA emphasized three points:
- The critical problem is a probability that Campylobacter is erroneously classified by NARMS as resistant when it is really susceptible. The breakpoint used to classify Campylobacter as resistant has not been correlated with clinical effectiveness of the drug. The breakpoint of 4 μg/ml was borrowed from other Enterobacteriaceae and was previously used just to monitor shifts in susceptibility. Two studies, including a national Centers for Disease Control and Prevention case-control study, show that people infected with supposedly resistant Campylobacter respond favorably to treatment with ciprofloxacin.
- It is not reasonable to attribute changes in the human prevalence of decreased susceptible Campylobacter on enrofloxacin use in poultry when, during the same time period of 1998-2000, the prevalence in poultry stayed the same.
- CDC case-control studies and a Minnesota study demonstrate that about 70 percent of the human-origin Campylobacter with decreased susceptibility is associated with foreign travel or treatment with a fluoroquinolone prior to culturing. And not all the remaining 30 percent is associated with chicken consumption. So the AVMA believes that withdrawal of the poultry approval would have a negligible effect, if any, on resistance in humans.