Antibiotics in first year of life may boost risk of childhood asthma: study

13/03/2006:-   TORONTO (CP) - Children given antibiotics in the first year of life may have a higher risk of developing asthma - although there is no evidence the drugs are directly responsible for causing the increasingly common disease, Canadian researchers say.

In a combined analysis of seven studies involving more than 12,000 youngsters, researchers at the University of British Columbia found that those prescribed antibiotics before their first birthday were more than twice as likely as untreated kids to develop asthma in childhood.

Furthermore, multiple exposure to antibiotics appeared to bump up the risk even higher - 16 per cent for every course of the drugs taken before age one, said co-principal investigator Carlo Marra, a professor of pharmaceutical science at the University of British Columbia.

Young children are often prescribed antibiotics for upper respiratory and middle-ear infections, even though many of those diseases turn out to be viral in origin. Antibiotics work only against bacteria.

"It appears that it is certainly possible that there is an association" between early antibiotic use and subsequent asthma, Marra said Monday from Vancouver. "Given that, it makes even more sense for people to use antibiotics judiciously. Not, 'Don't use antibiotics,' but only use them when they're necessary."

Still, Marra said "you have to be careful not to over-interpret the findings. . . . This is more evidence that there is potential adverse events associated with (antibiotics), asthma being one of them.

"But can we say for certain antibiotics cause asthma? No we can't."

What the drugs may do is contribute to a state of excess hygiene, which is a possible reason for rising rates of childhood asthma in Canada and other western countries. The "hygiene hypothesis" suggests that one reason behind the asthma epidemic is that children have too little exposure to microbes, in part because of widespread antibiotic use.

Limited exposure to germs can lead to an over-sensitive immune system, which mounts an over-the-top response to such non-threatening agents as pollen and dust mites. The result is an allergic reaction, which in some people can include the airway inflammation that's the hallmark of asthma.

About 15 per cent of Canadian children develop asthma, a rate double that of 15 to 20 years ago, said Dr. Felix Ratjen, chief of respirology medicine at Toronto's Hospital for Sick Children.

Commenting on the study published Tuesday in the journal Chest, Ratjen said the findings are not definitive because there are so many factors that could contribute to asthma.

"This is just an interesting observation that may or may not be true and the data are not convincing in one way or another," said Ratjen, who was not involved in the study.

Teasing out the role of antibiotics would be a complex task, said Ratjen, noting that some babies who come to the doctor wheezing - and are treated for a respiratory infection - are actually exhibiting the first signs of asthma and get misdiagnosed.

He cautioned that parents should not avoid antibiotics for their children - when necessary - because of a fear the medication may make them prone to asthma.

"In terms of antibiotics, that can be rather risky because certainly antibiotics are very important in fighting bacterial infections. And if a child has a bacterial infection and is not treated, this child will be at risk."

Toronto allergist Dr. Mark Greenwald, vice-president of the Asthma Society of Canada, said the analysis raises lots of questions about society's possible role in promoting asthma, which afflicts about 3.3 million Canadians of all ages.

"What is interesting is the theoretical stuff: Are we too clean? Are we using too many antibiotics? Should kids go through a number of infections and survive them?

"We know that there are too much antibiotics out there anyway," Greenwald said. "So are we compounding our own problems? It's a question, not an answer."

That's one of the issues Marra's team will try to tackle in a study of 200,000 B.C. infants, who will be followed after birth to look at the incidence of asthma and possible causative factors. Among the questions researchers will ask is: if antibiotics do contribute to asthma, are some classes of the drugs bigger culprits than others?

"Certainly based upon the evidence we have today, there very well may be an association and folks should be cognizant that we use too many antibiotics now," Marra said. "I'm not convinced there isn't a causation from what we found."
 
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