Azithromycin Safety During Breastfeeding
Azithromycin is classified as "probably safe" during breastfeeding and can be used when clinically indicated, though it should ideally be avoided during the first 13 days postpartum due to a very low risk of infantile hypertrophic pyloric stenosis. 1
Safety Classification and Timing Considerations
The European Respiratory Society/Thoracic Society of Australia and New Zealand (ERS/TSANZ) guidelines classify azithromycin as "probably safe" for breastfeeding mothers, which represents a high level of safety designation for antibiotics during lactation 1, 2
The critical timing caveat: There is a very low risk of hypertrophic pyloric stenosis in infants exposed to macrolides (including azithromycin) during the first 13 days of breastfeeding, but this risk does not persist after 2 weeks 1, 2
The FDA classifies azithromycin as Pregnancy Category B, and the drug label states "it is not known whether azithromycin is excreted in human milk" and recommends caution when administered to nursing women 3
Infant Exposure and Risk Assessment
Research demonstrates that the median estimated relative cumulative infant dose is 15.7% of the maternal dose (95% prediction interval: 2.0 to 27.8%), which exceeds the commonly recommended 10% safety limit 4
Despite this higher-than-typical exposure, the absolute infant dose remains relatively low at a median of 4.5 mg/kg (95% prediction interval: 0.6 to 7.0 mg/kg) 4
The worst-case number needed to harm for hypertrophic pyloric stenosis is estimated at 60 infants, indicating this remains a rare complication even during the high-risk first two weeks 4
Clinical Decision Algorithm
When azithromycin is indicated for a breastfeeding mother:
If the infant is >2 weeks old: Prescribe azithromycin without hesitation, as the pyloric stenosis risk no longer applies 1
If the infant is <13 days old: Consider alternative antibiotics first (amoxicillin, cephalosporins, or erythromycin), but if azithromycin is specifically indicated for the maternal infection, the benefits typically outweigh the very low risk 2, 5
Monitor all breastfed infants for gastrointestinal effects (diarrhea, altered bowel patterns) due to potential alteration of intestinal flora 1, 2
Important Monitoring Considerations
All systemic antibiotics, including azithromycin, will be present in breast milk and could cause falsely negative cultures if the breastfed infant develops fever requiring evaluation 1
Breastfed infants should be monitored for mild gastrointestinal disturbances, though serious adverse events are rare 2
Most antibiotics used in clinical practice are considered suitable during breastfeeding when the pharmacokinetic profile is properly considered 6
Common Pitfalls to Avoid
Do not automatically discontinue breastfeeding when azithromycin is prescribed—the lack of accurate information often leads healthcare professionals to unnecessarily suspend breastfeeding 7, 6
Do not confuse the timing-specific risk: The pyloric stenosis risk is confined to the first 13 days postpartum; after 2 weeks, this concern is no longer relevant 1
Do not assume all macrolides carry equal risk: While azithromycin, clarithromycin, and erythromycin all share the early postpartum pyloric stenosis risk, they are otherwise considered safe options for penicillin-allergic patients 1, 2