June 11, 2007 -- Infants who receive antibiotics in their first year of life are more likely to develop asthma by age 7, and multiple courses of the drugs boost the risk more, a Canadian study suggests.
"In children receiving five or more courses of antibiotics in the first year, the risk of asthma was 1.5 times more likely than in children getting no antibiotics [during their first year]," study researcher Anita Kozyrskyj, PhD, tells WebMD. Kozyrskyj is associate professor of pharmacy and medicine at the University of Manitoba in Winnipeg, Canada.
The study was published in the June issue of the journal Chest.
"The link between antibiotics and asthma was seen in children born to mothers without asthma, who are considered at low risk," Kozyrskyj says. And the link held even after other risk factors were taken into account. However, the study shows having a dog in the household while the child is a baby confers a protective effect.
Asthma affects almost 5 million children under age 18 in the U.S., according to the American Academy of Allergy Asthma & Immunology, including 1.3 million children under age 5.
Antibiotics and Asthma Risk
The new research adds to an ongoing debate in recent years about the effect early antibiotics may have on a child's risk of developing asthma. Kozyrskyj says research results are mixed; some studies, like hers, show an association (but not necessarily cause and effect), while other studies do not.
A report released in 2006 that analyzed five different studies found that infants who got even one course of antibiotics during their first year may have double the risk of getting asthma later in childhood than babies who received no antibiotics for their first 12 months.
Kozyrskyj and her colleagues used a prescription database from the University of Manitoba and McGill University in Montreal to monitor the antibiotic use of 13,116 children from birth to age 7 years. They noted in particular the antibiotic use in the first year and whether the child had developed asthma by age 7.
When antibiotics were given, the reason was noted -- including lower respiratory tract infections (such as bronchitis), upper respiratory tract infections (such as ear infection), or nonrespiratory tract infection (such as urinary or skin infections). Researchers also noted each child's risk factors for getting asthma, such as having a mother with asthma.
Besides looking at the records, "we also sent out a one-page survey to ask additional questions," Kozyrskyj says. Researchers asked parents to note whether children were exposed to tobacco smoke as infants and whether the household included dogs or cats.
Within the group, 6% of the children had asthma by age 7. Antibiotic use was widespread, with 65% of the children having been prescribed at least one course of the medication during the first year of life.
The researchers found that for children who got the medications for nonrespiratory infections, the risk of getting asthma by age 7 was nearly twice as likely as children who got no antibiotics from birth to age 1 year.
The finding strengthens the idea that early antibiotic use and asthma are linked, Kozyrskyj says. "In that case you can't say maybe [the asthma] was due to the respiratory tract infection."
If the household of children taking multiple medication courses did not have a dog, the children's risk of getting asthma doubled, she found. "Dogs bring in different germs," she says. And that could strengthen a child's immunity.
In the study, cats didn't offer the same effect, she says, and may actually boost risk, although the evidence for that in the study was weak.
Explaining the Link
Exactly why the early antibiotic use may boost asthma risk later isn't certain, Kozyrskyj says. She speculates that because antibiotics can kill off the microflora (natural bacteria) in your intestinal tract, "it may change your immune system, making you more vulnerable to developing asthma."
Still, she emphasizes, asthma is a complex disease. "It's also genetic. We've identified one factor." But many factors underlie the condition, she says.
One strength of the study, according to an allergist not involved in it, is that the researchers found the link held up between antibiotics and asthma not just for the children who were treated for respiratory infections.
"The researchers make the argument that these kids [treated for nonrespiratory infections] were not destined for asthma" yet developed it after the antibiotic treatment, says William Anderson, MD, a board-certified allergist in Bellingham, Wash.
Advice for Parents
When your child has an infection and your child's doctor suggests an antibiotic, what’s best? "A parent might question the need for an antibiotic," Anderson says, and ask about other options. But, he emphasizes, "there are cases when a kid really needs an antibiotic."
Kozyrskyj agrees that antibiotics are sometimes crucial, although she notes the trend among physicians and pediatric groups is to encourage more judicious use of antibiotics due to antibiotic resistance and other potential problems.
But, Kozyrskyj says, if your child does need an antibiotic, you can ask your child's doctor if it is possible to use a narrow-spectrum antibiotic rather than a broad-spectrum (effective against a wider range of bacteria) cephalosporin (a class of antibiotics). In her study, she also found that broad-spectrum cephalosporin antibiotics (such as Ceftin and Cefzil) boosted the risk of getting asthma more than other antibiotics.
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