Is azithromycin (macrolide antibiotic) safe to use during breastfeeding?

Azithromycin and Breastfeeding

Azithromycin is probably safe to use during breastfeeding, but should be avoided during the first 13 days postpartum due to a very low risk of hypertrophic pyloric stenosis in the infant. 1

Safety Classification and Timing

• The European Respiratory Society/Thoracic Society of Australia and New Zealand (ERS/TSANZ) classifies azithromycin as "probably safe" during breastfeeding with FDA Category B1 designation. 1, 2

• Critical timing consideration: An epidemiological study demonstrates a very low but measurable risk of hypertrophic pyloric stenosis in infants exposed to macrolides (including azithromycin) during the first 13 days of breastfeeding only—this risk does not persist after 2 weeks. 1, 2

• After the initial 2-week postpartum period, azithromycin can be used without this specific concern. 1

Infant Exposure and Monitoring

• Pharmacokinetic data from African mothers given 2g azithromycin during labor showed that the median cumulative infant dose was 15.7% of the maternal dose (range 2.0-27.8%), which exceeds the traditional 10% safety threshold. 3

• Despite this higher-than-ideal transfer rate, the absolute infant dose remains relatively low at 4.5 mg/kg (range 0.6-7.0 mg/kg). 3

• Monitor breastfed infants for:

  • Gastrointestinal effects (diarrhea, altered stool patterns) due to disruption of intestinal flora 1, 2
  • Signs of pyloric stenosis if used in the first 2 weeks (projectile vomiting, poor feeding) 1

Clinical Decision Algorithm

If the infant is <13 days old:

• Consider alternative antibiotics (amoxicillin/clavulanic acid is "compatible" and preferred) 1, 2, 4
• If azithromycin is absolutely necessary and no safer alternative exists, use with heightened vigilance for pyloric stenosis symptoms 1

If the infant is >2 weeks old:

• Azithromycin can be used safely with standard monitoring for GI effects 1, 2
• The pyloric stenosis risk no longer applies after this timeframe 1

Important Caveats

• Like all systemic antibiotics, azithromycin in breast milk could cause falsely negative bacterial cultures if the infant develops fever requiring sepsis evaluation. 1, 2

• The FDA label states "it is not known whether azithromycin is excreted in human milk" and recommends caution, though subsequent research has confirmed breast milk transfer. 5, 3

• Most antibiotics are considered compatible with breastfeeding, and azithromycin's "probably safe" designation places it in a reasonable middle ground—safer than fluoroquinolones but slightly less preferred than penicillins or cephalosporins. 2, 6, 7