Fewer children in the U.S. are being prescribed antibiotics to treat respiratory tract infections, a new study suggests.

Doctors appear to be largely following guidelines for reducing unnecessary use of antibiotics, Dr. Carlos Grijalva of Vanderbilt University in Tennessee and colleagues reported in Tuesday's issue of JAMA.

"Our results indicate that overall antibiotic prescription rates have decreased significantly," the researchers concluded after analyzing data from two large federal surveys.

"These changes coincided with efforts to reduce inappropriate antibiotic prescribing and the initiation of routine infant immunization with pneumococcal conjugate vaccine. Further efforts to improve antibiotic selection are needed."

The pneumococcal conjugate vaccine protects against seven strains of Streptococcus pneumoniae that can cause ear infections.

Among children younger than five, antibiotic prescriptions for acute respiratory tract infections such as colds, flu, sore throats and ear infections fell 36 per cent between 1995 and 2006, the researchers found.

For the same age group, annual visits to doctors for ear infections also decreased by 33 per cent, and use of antibiotics for ear infections fell 36 per cent over the 12-year study period.

More broad-spectrum antibiotic prescriptions

Despite the overall decline, prescriptions for broad-spectrum antibiotics, such as azithromycin, in young children for respiratory and middle ear infections increased from 16 prescriptions per 1,000 population in 1995-1996 to 140 per 1,000 in 2005-2006.

The data suggested azithromycin has become the most commonly prescribed macrolide type of antibi otic for ear infections and respiratory infections.

Some of the azithromycin prescriptions may be unnecessary, the researchers said.

"Although the ease of administration is an advantage, a recent meta-analysis of randomized and quasi-randomized controlled trials showed that azithromycin efficacy against bronchitis or pneumonia was not better than amoxicillin or amoxicillin/clavulanic acid," the researchers said.

Recent guidelines for community-acquired pneumonia in adults suggest prescribing azithromycin alone only for previously healthy patients without risk factors for drug-resistant strep, the study's authors noted.

The study was funded by the U.S. Centers for Disease Control and Prevention. Some of the study's authors reported past financial ties with pharmaceutical companies.