Agricultural Use of Antibiotics Prompts Human Health Concerns: FDA Bans Controversial Poultry Drug

Patti Truant

Nations Health. 2005;35(10) 

Although the U.S. Food and Drug Administration recently removed a controversial poultry antibiotic from the market amid evidence of increased antibiotic resistance in humans, experts say that a more rigorous, multi-disciplinary approach is needed to preserve the effectiveness of important antibiotics.

With growing concerns about antibiotic resistance as well as the difficulties of developing new and effective drugs, the banning of the antibiotic enrofloxacin for use in poultry may be more of an indication of a problem than a solution in itself.

After a five-year long struggle between FDA and the Bayer Corporation, the company's enrofloxacin drug, known as Baytril, was banned for use in poultry in September. The drug is a fluoroquinolone antibiotic that is very similar to the human drug ciprofloxacin, raising concerns that the human drug could become resistant to common infections.

Ciprofloxacin, marketed by Bayer as Cipro, is used to treat a wide range of ailments including food poisoning and urinary tract infections. Since 1995, when Baytril was approved for use in poultry, bacterial resistance to Cipro has grown to an estimated 21 percent, according to David Wallinga, MD, MPA, director of the Antibiotic Resistance Project at the Institute for Agriculture and Trade Policy.

Antibiotic resistance is a complex problem that requires greater cooperation between regulatory agencies, agriculture, the medical field and the public as a whole, said Thomas Fekete, MD, a professor of medicine and infectious disease at Temple University.

"No one is being allowed to execute the big vision," he said. "It is being executed at the regulations level. At the end of the day, it may not be enough. We may need a more robust approach rather than 'nickel and diming' it with one drug on (the market) and one drug off. It's an issue the society as a whole has to face."

Overuse of antibiotics in livestock can harm human health by facilitating antibiotic-resistant strains of infections. A November study found that humans can even be exposed to agriculturally used antibiotics in their vegetables. The study, published online in the Journal of Environmental Quality, found that when corn, cabbage and green onions were grown in fertilizer derived from the manure of antibiotic-fed pigs, the vegetables absorbed the antibiotics.

Karen Florini, JD, a senior attorney at Environmental Defense and chairwoman of Keep Antibiotics Working, a Chicago-based campaign to eliminate the overuse and misuse of antibiotics, said she was pleased that Baytril was banned for widespread agricultural use because it is a step in the right direction, albeit a small one.

"The good news is that the FDA has shown, for the first time ever, that it can actually take an agricultural antibiotic off the market based on antibiotic resistance concerns," Florini said. "The bad news is that it took the agency five years to deal with this one class of antibiotic for just poultry."

Florini added that there are seven other important antibiotics currently being used in feed animals.

"It's essential for FDA and Congress to pick up the pace," she said.

Abbot Labs withdrew its version of the fluoroquinolone antibiotic in 2000 after the FDA announced its intention to ban it. After that, Bayer was the only company still making the drug, according to Keep Antibiotics Working.

Bayer challenged FDA and asked for a formal evidentiary hearing on its plan to remove the drug for use in poultry. Bayer was allowed to keep its drug on the market during the process. In July, FDA issued its final decision on the issue, ordering the end of the drug's use. Bayer chose not to appeal, and the ban went into effect on Sept. 12.

The widespread use of antibiotics in agriculture is problematic because the more a drug is used, the greater likelihood that strains of bacteria grow resistant to it, Wallinga said.

"Unlike in humans where these drugs have been used very judiciously and only for sick people, fluoroquinolones in poultry have been administered on a flock-wide basis when only a few birds might be sick," he said. "It's clear that fluoroquinolone use in poultry is unnecessary. Producers were making do without it previously, and many make do with(out) it now. It's simply foolish to risk such a valuable antibiotic to human medicine in poultry flocks."

According to the Union of Concerned Scientists, an estimated 70 percent of antibiotics in the U.S. are fed to animals raised for human consumption to promote growth and prevent illness due to overcrowded and unsanitary conditions.

Chickens and turkeys have Campylobacter jejuni bacteria in their digestive tracts, some of which is not killed by Baytril-like drugs, which were approved by FDA to control deaths associated with Escherichia coli, another kind of bacteria. The bacteria that remain become resistant to the drug, and can be passed on to people through the transportation, slaughter and preparation of poultry.

Campylobacter is a significant source of food poisoning, and reductions in the effectiveness of the fluoroquinolones used to treat the infection can lead to prolonged illness and increased risk of complications such as reactive arthritis and blood stream infections, according to a spokeswoman for FDA's Center for Veterinary Medicine.

"The proportion of Campylobacter infections that are resistant to fluoroquinolones has increased significantly since the FDA approved the use of fluoroquinolones in poultry in the U.S.," said the spokeswoman, who asked not to be named.

Wallinga said that by 1999, one year before the FDA first proposed a ban on fluoroquinolones, Campylobacter resistance to Cipro was up to 14 percent. The latest data, from 2002, shows resistance levels of 21 percent.

However, Sam W. Joseph, PhD, professor of cell biology and molecular genetics at the University of Maryland, said it is hard to prove conclusively that the human resistance came from the use of Baytril in agriculture.

"One of the difficult things to do is to prove that an organism in a human comes from a chicken," he said. "That's one of the things the Bayer people kept emphasizing to make it difficult for the FDA to take Baytril off the market."

It is also important to note the role of other factors in antibiotic resistance, such as the overprescribing of antibiotics for human illnesses, Joseph said. The Centers for Disease Control and Prevention has been working in recent years to reduce antibiotic overprescribing through education campaigns aimed at physicians and health providers, with some success: A 2003 study in Pediatrics found that the number of antibiotic prescriptions written for children had fallen because of doctor and patient awareness of the issue.

The need to maintain the effectiveness of current antibiotics is magnified by the difficulty of obtaining new antibiotics, Joseph said.

"Drug companies for some time now have not been bringing out new antibiotics," Joseph said. "The bottom line is money. Drug companies estimate it costs $1 billion to develop a new drug, and if they don't see profit with their investment, they are unlikely to get involved."

Even if drug companies do produce new kinds of antibiotics, Fekete said this it is not the solution to antibiotic resistance concerns.

"It's sort of like you're in credit card debt and you get a lot of offers for lower interest rates, and you can shuffle the balances around to different cards, but at the end of the day you still have the same debt," Fekete said. "That's how I think about this problem. Getting new drugs is one part of the solution: They keep you out of trouble for a while, but they don't really solve the problems."

There is legislation currently before Congress that would phase out the agricultural use of certain antibiotics that are important to human medicine. The Preservation of Antibiotics for Medical Treatment Act, also known as H.R. 2562 and S. 742, would ban eight classes of antibiotics from being used in animal feed.

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