Parents and pediatricians will often reach for antibiotics to treat middle-ear infections, strep throat, fevers and other common ailments of childhood. But new research suggests that doing so, and prescribing broad-spectrum antibiotics in particular, increases those children’s risk of obesity, at least in early childhood.

A new study finds that babies who got broad-spectrum antibiotics in their first two years of life, or who were prescribed four or more courses of antibiotics in that period, were more likely to be obese at some point between their second and fifth birthdays than were those who had taken no antibiotics, or who were treated with medications designed to target a narrow spectrum of disease-causing bacteria.

Broad-spectrum antibiotics – including amoxicillin, tetracycline, streptomycin, moxifloxacin and ciprofloxacin – are intended for treatment of major systemic infections, in cases where the bacteria causing the illness has not been identified, or where a patient is under attack by a strain of bacteria resistant to standard antibiotics. While they can be highly effective, their antibiotic action is indiscriminate, and beneficial bacteria in the body are often killed off as collateral damage.

The latest study tapped the medical records of 64,580 babies and children in and around Philadelphia. It was published Monday in the journal JAMA Pediatrics.

The heightened risk of obesity linked to antibiotic use was not huge: Babies who got wide-spectrum antibiotics in their first two years were about 11 percent more likely to be obese between 2 and 5 than were those who got no such drugs. Babies who had four or more courses of any antibiotics in the first two years were also 11 percent more likely to be obese in early childhood than those who had had fewer exposures to antibiotics.

But among children who had four or more antibiotics prescriptions, including at least one wide-spectrum antibiotic, the risk of obesity rose to 17 percent.