Erythromycin: update on known risk of infantile hypertrophic pyloric stenosis
A recent European review of safety data recommended information on the magnitude of the increased risk of this known side-effect be added to the product information, and to reflect that the risk is highest in the first 14 days after birth (incidence 2.6% [95% CI 1.5 to 4.2]).
Source:
Medicines and Healthcare products Regulatory Agency