Kate Johnson

September 18, 2014

WASHINGTON — Newborns exposed to azithromycin in the first 6 weeks of life have a significantly increased risk of developing hypertrophic pyloric stenosis, a new study suggests.

"Practitioners must carefully weigh the risks and benefits when prescribing azithromycin, particularly to male infants, in the first few weeks of life," said lead investigator Matthew Eberly, MD, from the Uniformed Services University of the Health Sciences, in Bethesda, Maryland. "These infants should be monitored for signs and symptoms of pyloric stenosis for 6 weeks following treatment."

The results of the study were presented here at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

"We have been seeing a rise in the prescriptions of azithromycin given to infants less than 90 days in the US over the past 10 years, and I suspect that many of these are for prophylaxis for pertussis," Dr. Eberly told Medscape Medical News.

"We know that erythromycin is associated with the development of pyloric stenosis. After this discovery was made in 1999, another macrolide antibiotic — azithromycin — replaced erythromycin as the prophylaxis of choice in infants exposed to pertussis. However, no large studies have looked at the potential risk," he explained.

Replacing Erythromycin

The study retrospectively evaluated all children registered in the TRICARE Management Activity military health system database. Investigators identified children less than 90 days old with infantile pyloric stenosis using specific ICD-9CM and CPT codes for diagnosis and surgical correction. They used outpatient prescription to identify infants of this age who were prescribed either azithromycin or erythromycin.

For the 4875 infants prescribed azithromycin, there was an 8-fold increased risk of developing the condition for those exposed in the first 14 days (P < .001) and a 3-fold increased risk for those exposed between days 15 and 42 (P = .15).

Of the 3998 infants exposed between days 43 and 90, there were no cases of infantile hypertrophic pyloric stenosis.

As expected, the risk for infantile hypertrophic pyloric stenosis was much higher in infants exposed to erythromycin. The risk was 13-fold for infants exposed in the first 14 days of life (P < .001) and 4-fold for those exposed between days 15 and 90 (P = .002). There were 3 cases among the 1076 infants exposed between days 43 and 90 (odds ratio, 0.22; P = .76).

As has been reported previously, male sex conferred a higher risk of developing infantile hypertrophic pyloric stenosis. All 8 patients in the azithromycin-exposed group were male, as were 14 of the 17 (82.4%) of the erythromycin-exposed patients.

Pyloromyotomy was performed a median of 13 days following exposure to erythromycin, and a median of 29.5 days following exposure to azithromycin.

Asked by Medscape Medical News to comment on the study, Penny Heaton, MD, a pediatric infectious diseases specialist with the Bill & Melinda Gates Foundation and a member of the ICAAC program committee said, "Pyloric stenosis was added to the azithromycin package insert as a potential side effect a year or so ago. As with other interventions, physicians will need to weigh the benefits and risks when considering whether to use azithromycin in very young infants."

Dr. Eberly and Dr. Heaton report no relevant financial relationships.

54th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): Abstract G-993. Presented September 7, 2014.

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