Azithromycin Safety During Breastfeeding
Azithromycin is probably safe to use during breastfeeding, with the important caveat that it should be avoided during the first 13 days postpartum if possible 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" during breastfeeding, which is one step below "compatible" but still indicates acceptable use. 1
The critical timing restriction is the first 13 days postpartum: epidemiological studies demonstrate 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
After the first 2 weeks postpartum, azithromycin can be used with standard monitoring precautions. 2
FDA Labeling and Drug Transfer
The FDA label states "it is not known whether azithromycin is excreted in human milk" and recommends that "caution should be exercised when azithromycin is administered to a nursing woman." 3
Research demonstrates that azithromycin does transfer into breast milk, with median estimated relative cumulative infant doses of 15.7% of the maternal dose, which exceeds the generally recommended 10% safety threshold. 4
Despite this higher transfer rate, the absolute infant dose remains relatively low at approximately 4.5 mg/kg. 4
Infant Monitoring Requirements
Monitor all breastfed infants for gastrointestinal effects, particularly diarrhea or changes in stool pattern, due to alteration of intestinal flora. 1, 2
Be aware that antibiotics in breast milk could potentially cause falsely negative cultures if the breastfed infant develops fever requiring evaluation. 1, 2
Watch specifically for signs of pyloric stenosis (projectile vomiting, poor feeding) if azithromycin must be used in the first 2 weeks postpartum. 1
Clinical Decision Algorithm
If treatment is needed in the first 13 days postpartum:
- Consider alternative antibiotics that are classified as "compatible" rather than "probably safe," such as amoxicillin or cephalosporins. 2, 5
- If azithromycin is clinically necessary (e.g., for penicillin-allergic patients), use it but counsel parents about pyloric stenosis warning signs. 2, 5
If treatment is needed after 2 weeks postpartum:
- Azithromycin can be used with standard infant monitoring for gastrointestinal effects. 1, 2
- The American Academy of Dermatology suggests azithromycin as a safe alternative, particularly for penicillin-allergic patients. 2
Common Pitfalls to Avoid
Do not assume all macrolides have identical safety profiles: while azithromycin, erythromycin, and clarithromycin all carry the pyloric stenosis risk in the first 13 days, their other characteristics differ. 1
Do not unnecessarily avoid azithromycin after 2 weeks postpartum: the pyloric stenosis risk is time-limited to the first 13 days, and continued avoidance after this period is not evidence-based. 1, 2
The worst-case number needed to harm for pyloric stenosis is estimated at 60, meaning this remains a rare complication even during the high-risk period. 4