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TUESDAY, Aug. 10 (HealthDayNews) -- Alternating the most commonly used antibiotics -- a method called cycling -- to stop the spread of antibiotic-resistant bacteria probably won't work.

A University of Washington study reports the disappointing results in this week's issue of the Proceedings of the National Academy of Sciences.

Instead of cycling -- alternating between two or more classes of antibiotics as often as every few months -- this study suggests an approach called mixing, where a patient is randomly administered two or more antibiotics.

Cycling is a new approach that's currently undergoing clinical trials in patients. The theory behind cycling is that, just as a pathogen begins to develop resistance to a particular antibiotic, a new antibiotic is introduced and the pathogen has to start all over again in building resistance to the new antibiotic.

But pathogens actually encounter new antibiotics more frequently with mixing than with cycling, according to this study, based on numerical models that examined how microbial infections spread in hospitals and how microbes develop antibiotic resistance.

Mixing is already relatively common in hospitals, even though it's not planned, the study authors noted. That's because individual doctors develop preferences for the kinds of antibiotics they prescribe, meaning that patients receive a variety of antibiotics at random.

"If the cycling trials that are under way don't work, we'll know why they don't," study author Carl Bergstrom, an assistant professor of biology, said in a prepared statement.

"And if they do work, the people conducting the trials are going to have to do further investigation on why they are working, because the rationale that we've been using for cycling doesn't hold true," Bergstrom said.

More information

The American Academy of Family Physicians has more about antibiotics.

(SOURCE: University of Washington, news release, Aug. 9, 2004)

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