Giving young infants the antibiotic erythromycin -- particularly in the first 2 weeks of life -- raises their risk of a gastrointestinal complication that may require surgery.

Investigators also found a possible association between a complication called infantile hypertrophic pyloric stenosis (IHPS) and a mother's use of certain antibiotics in the last 10 weeks of pregnancy.

IHPS occurs when the pylorus, a tube leading from the stomach to the small intestine, becomes enlarged. This blocks the stomach's outlet and causes projectile vomiting and subsequent weight loss and dehydration in infants.

IHPS normally arises when babies are about one month old and it is the most common cause of abdominal surgery in infancy.

In most cases, the newborns were given the antibiotic because their mothers had chlamydia infections.

Mahon's team also saw some evidence that a mother's use of erythromycin or one of two related antibiotics-Zithromax and Biaxin be linked to IHPS, but the finding was not statistically significant.

There was no risk associated with topical erythromycin ointments given to infants for pink eye, the report indicates.

This study confirms an association between systemic erythromycin in infants and subsequent IHPS, with the highest risk in the first 2 weeks of age. The authors add that maternal antibiotic use and IHPS should be studied further.

Doctors should use caution in prescribing the antibiotic in early infancy, the researchers urge. And when it is prescribed, prudence dictates that parents should be informed of the risk and symptoms of IHPS.

Journal of Pediatrics September 2001;139:380-384