"This is definitely a good news, bad news report," says Dr. Richard Besser, director of the U.S. Centers for Disease Control and Prevention (CDC) Campaign for Appropriate Antibiotic Use in the Community.

Overuse of antibiotics is bad because it hastens the development of resistant strains of bacteria, Besser and other experts say. It's especially troublesome when antibiotics are used to treat the common cold and other ailments caused by viruses. Antibiotics kill bacteria but are shrugged off by viruses.

The report, by Dr. Michael A. Steinman and colleagues at the San Francisco Veterans Affairs Medical Center, compares data from the National Ambulatory Medical Care Survey for 1991-1992 and 1998-1999. It finds visits to doctors in which an antibiotic was prescribed for adults dropped from 13 percent in the earlier period to 10 percent in the later period. For children, the decrease was from 33 percent to 22 percent. Overall, the number of antibiotic prescriptions declined from 230 million in the earlier period to 190 million in 1998-1999, says a report in the April 1 issue of the Annals of Internal Medicine.

But at the same time, use of broad-spectrum antibiotics doubled in both adults and children, and they were often prescribed for bronchitis and other respiratory infections, against which they are almost always useless.

"The fact that we are using more and more broad-spectrum antibiotics may signal an impending crisis in antibiotic resistance," says Steinman, who is a fellow in geriatrics in the VA center's Quality Scholar Program.

Signs of such a crisis are starting to appear, Steinman says. "In my clinical practice today, I was taking care of a patient with a highly resistant urinary tract infection," he says. "What you are forced to do in such a case is rely on the smaller and smaller number of antibiotics that are still active against that infection."

Pharmaceutical company advertising aimed at consumers plays a notable role in the inappropriate use of broad-spectrum antibiotics, Besser and Steinman say.

Other factors are at work, such as "possible concern among physicians about missing that one-in-a-million case where a broad spectrum antibiotic might be useful," Steinman says.

But there are clear effects of pharmaceutical companies promoting the use of broad-spectrum antibiotics because "they are for the most part still under patent and therefore lucrative for the manufacturers," he says. Often, patients demand that a doctor prescribe a drug they have seen advertised, Steinman says.

The CDC will be part of a national public service advertising campaign to promote appropriate antibiotic use that will be launched in the autumn, Besser says.

"But I don't think it will have much effect, considering the incredible amount of money being spent by the pharmaceutical industry," he says.

Yet he hopes the campaign will have some effect. "What we are hoping is that a patient will not come into a physician's office and say, 'I was watching Sesame Street this morning and want Z-Pack.'" That is a name Pfizer gives to its broad-spectrum antibiotic, Zithromax, which is marketed on that children's television show.

More information

Advice on what you can do to prevent unnecessary antibiotic use is offered by the Alliance for the Prudent Use of Antibiotics or the U.S. Centers for Disease Control and Prevention.