A preterm neonate at 30 weeks receives erythromycin for Ureaplasma urealyticum pneumonia. Two days later, the nursing staff notes projectile vomiting and abdominal distension. Abdominal X-ray shows a distended stomach with a 'double bubble' appearance. Which adverse effect of erythromycin has likely caused this?

• A Erythromycin-induced hepatotoxicity causing cholestatic jaundice
• B Erythromycin-induced gut dysmotility through antibiotic disruption of normal microbiome
• C Erythromycin acts as a motilin agonist, causing hypertrophic pyloric stenosis in neonates ✓
• D QT prolongation causing cardiac dysfunction and secondary gastroparesis

Explanation

Erythromycin is a well-documented risk factor for hypertrophic pyloric stenosis (HPS) in neonates, particularly when administered in the first 2 weeks of life. Erythromycin is a potent motilin receptor agonist; in neonates, motilin receptor activation causes excessive pyloric muscle contraction, leading to pyloric hypertrophy and the development of HPS. This association has been documented in multiple epidemiological studies. The risk is highest with oral erythromycin in the first 2 weeks of life. Double bubble sign represents a distended stomach (not true double bubble of duodenal atresia), pointing to gastric outlet obstruction from pyloric stenosis.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.