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Antibiotic Resistance: Are Animals Part of the Problem?

By Ori Twersky
WebMD Health News

April 19, 2000 (Washington) -- Could the food on your table be partially responsible for society's growing resistance to even the most powerful of antibiotics available today? That is what some experts say, and a question that the FDA now also says probably deserves an answer, despite the lack of any case reports.

As part of that effort, the FDA said Wednesday it would start investigating. More specifically, the agency said, its investigation would focus on the possible association between the development of antibiotic-resistant Enterococcus faecium (E. faecium) in humans and the use of an antibiotic called virginiamycin in the treatment of food-producing animals.

E. faecium is a supergerm that invades surgical wounds, causing potentially deadly abdominal, urinary tract, and heart valve infections. Virginiamycin has been widely used in the treatment of food-producing animals for about 26 years. It is generally fed as a preventive measure to turkeys, chicken, swine, and cattle, whether needed or not.

The rationale for this comparison is based on virginiamycin's similarity to the antibiotic Synercid, which the FDA approved in 1999 as a last-line treatment for E. faecium partly on the basis that it had never been used before in humans. But immediately after it was approved, strains of bacteria resistant to Synercid began emerging in hospitals, feeding both the speculation that the use of virginiamycin in animals may be responsible and the general notion that resistance can be transferred from animals to humans.

To be on the safe side, Frederick Angulo, PhD, DVM, advocates adopting a ban on the use of these antibiotics for the treatment of food-producing animals similar to the one already enacted by authorities in Europe. The potential problem is simply too great to ignore, says Angulo, a medical epidemiologist at the Centers for Disease Control and Prevention.

The stakes are large. These infections presently comprise an estimated 20% to 30% of the more than 2 million hospital-acquired infections per year in the U.S. And although the majority can be treated with an antibiotic called vancomycin, about 14% of these infections are now vancomycin resistant, leaving Synercid as basically the last-line defense for about 70,000 infections per year, according to CDC figures.

There is also now a new antibiotic called Zyvox, which the FDA approved Tuesday for the treatment of these infections. But it is not a magic bullet, and should be saved only for situations when there is no other choice, the FDA said at the time. Synercid and other antibiotics should remain the first line of defense, the FDA says.

But whether Synercid will remain an important treatment option could largely depend upon the results of the FDA's risk assessment. The millions spent on medicated animal feed by food producers each year have made drug makers reluctant to voluntarily surrender this market, say advocates of an antibiotic ban in the U.S.

"We live in a society of laws, and we will comply with any rules passed by the FDA," says Brian McGlynn, a spokesman for Pfizer, the maker of virginiamycin. However, he confirms, the drug maker does not agree with the "precautionary steps" taken in Europe.

Nonetheless, he adds, Pfizer does applaud the FDA's decision to conduct a risk assessment. It is a reflection of the FDA's commitment to applying a rigorous application of scientific evidence in the making of public policy, he says.

The FDA's risk assessment will begin with the collection of scientific data and other relevant information. The date of completion will largely depend upon the amount of evidence gathered by the agency during this period, the FDA says.

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