SALT LAKE CITY--A decade-long study in 10 hospitals has yielded new evidence that one of the main classes of antibiotics is losing its efficacy. The study, presented here 20 May at the general meeting of the American Society for Microbiology, shows that as hospital use of the so-called fluoroquinolones has risen sharply, so has bacterial resistance to these drugs.
Fluoroquinolones make up a broad category of widely used antibiotics. Its most popular member is ciprofloxacin or Cipro--the antibiotic of anthrax-slaying fame--which doctors prescribe to treat more than 15 kinds of bacterial infections. Experts have warned for some time that overuse of fluoroquinolones will lead to increased resistance, but cutting their use has been difficult. That's especially worrisome because a bug that becomes resistant to one fluoroquinolone usually survives the others as well.
Marcus Zervos and Ellie Hershberger of the William Beaumont Hospital in Royal Oak, Michigan, and colleagues at nine other hospitals tracked the use of all fluoroquinoles during the last decade, while also frequently testing the susceptibility of four infection-causing microbes--Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Proteus mirabilis--to ciprofloxacin. They found that in all but one hospital, fluoroquinolone use, expressed as the number of doses given to the average patient each day, had gone up--in one case by 264%. At the same time, the four bacteria had become less susceptible, and more so in the hospitals in which use had soared.
In the one hospital where antibiotic use had gone down, however, Cipro had lost little of its punch, and it had even become more effective in killing Pseudomonas. The decrease in Pseudomonas' susceptibility to Cipro in the other nine hospitals--which ranged from 4% to 45%--is particularly troublesome, the researchers say, since few other drugs can fight that microbe.
Colleagues say the study--one of several on rising resistance presented at the meeting--is another warning sign that doctors may soon find themselves without their most powerful weapons. And liberal prescription practices are just one cause of the problem, says Stuart Levy, a microbiologist at Tufts University in Boston and president of the Alliance for the Prudent Use of Antibiotics (APUA). Another major cause is the use of antibiotics as growth promoters in animal husbandry (Science, 5 May 2000, p. 792)--a practice that the APUA is hoping to get banned soon.
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