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FDA Rules Override Warnings About Drug

"They fought this tooth and nail. It took years," said Kirk Smith, an epidemiologist at the Minnesota Department of Health.

Finally, late in 2005, Bayer gave up, but not before fluoroquinolone resistance had spread even further.

A Question of Resistance

Microbes are constantly mutating, and some of those mutations happen to confer immunity to one drug or another. Exacerbating the problem, bacteria constantly exchange bits of DNA with each other, spreading that resistance.

Given those realities, experts agree that all antibiotics should be used judiciously.

"If a drug is used less, then less resistance emerges," said Patricia Griffin, chief of intestinal disease epidemiology for the CDC.

Prudence is especially important for medicines of last resort, which is why the cefquinome application stirred such a storm.

Cefquinome is a fourth-generation cephalosporin, the most recent of several steadily improving versions of the cephalosporin family of antibiotics. Only one medicine from that family has been approved in the United States -- a powerful human drug called cefepime (brand name Maxipime), which is the only effective treatment for serious infections in cancer patients and a reliable lifesaver against several other nearly invincible infections.

InterVet developed cefquinome to treat bovine respiratory disease, the most common disease in cattle. Recognizing the potential public health implications of using a close cousin of cefepime in animals, the FDA's Center for Veterinary Medicine, which oversees animal drug approvals, convened its expert advisers in September.

One of the first things the group learned was that more than a dozen medicines are already on the market for the respiratory syndrome, and all are still effective.

"If we have no susceptibility problem, why do we need one more new drug?" asked James E. Leggett Jr., a professor of medicine at Oregon Health & Science University, whom the FDA brought in as a consultant on the cefquinome question.

The panel also learned that the disease would be a relatively minor issue but for the stressful conditions under which U.S. cattle are raised, including high-density living spaces and routine shipment on crowded trains for hundreds or thousands of miles. Those "production dynamics" suppress the animals' immune systems, explained feedlot consultant Kelly Lechtenberg of Oakland, Neb., and virtually guarantee that bovine respiratory disease will be a major problem.

Yet Stephen Sundlof, head of the FDA's Veterinary Medicine Center, told the panel members that under agency rules they should ignore those issues and consider only the language in Guidance #152.

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