Antibiotics prescribed for infants within six months of birth may be contributing to increased rates of asthma, scientists say. The results of a new study suggest that babies who receive the medications are more than twice as likely to develop asthma than are children who did not take antibiotics. The findings were presented Tuesday at the annual meeting of the European Respiratory Society in Vienna.

Numerous studies have been designed to try and elucidate the relationship between childhood exposures and increased rates of asthma and allergies, often with conflicting results. In the new work, epidemiologist Christine Cole Johnson of the Henry Ford Hospital in Detroit and her colleagues followed 448 children from birth until they were tested by an allergist at the age of six or seven. About half of the subjects had received antibiotics at least once by the time they reached six months of age. The researchers found that these children were 2.5 times more likely to develop asthma than those who did not receive such treatment. "I'm not suggesting children shouldn't receive antibiotics," Johnson cautions. "But I believe we need to be more prudent in prescribing them for children at such an early age. In the past, many of them were prescribed unnecessarily, especially for viral infections like colds and the flu when they would have no effect anyway."

The scientists also reported a link between the medications and the development of allergies to pets, ragweed, grass and dust mites. They found that children who had taken antibiotics were 1.5 times as likely to develop allergies than children not given the drugs. The findings also support results published last year in the Journal of the American Medical Association, which indicated that early exposure to more than one pet lowers a child's risk of allergies. For children given antibiotics who lived with fewer than two pets, the risk of allergies rose slightly to 1.7 times that of kids who had not received antibiotics, whereas their risk of asthma increased to three times that of children who hadn't taken the drugs.