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

Azithromycin During Breastfeeding

Azithromycin is probably safe during breastfeeding, but should ideally be avoided during the first 13 days postpartum due to a very low risk of hypertrophic pyloric stenosis in the infant—after 2 weeks of infant age, this risk disappears and azithromycin can be used with standard monitoring. 1, 2

Safety Classification and Timing

• The European Respiratory Society classifies azithromycin as "probably safe" during breastfeeding, which is the second-highest safety designation for antibiotics during lactation 1, 2
• The FDA categorizes azithromycin as Pregnancy Category B, indicating no evidence of risk in human studies 1, 2
• The critical distinction is infant age: epidemiological studies demonstrate a very low risk of hypertrophic pyloric stenosis only when macrolides (including azithromycin) are used during the first 13 days of breastfeeding—this risk does NOT persist after 2 weeks 1, 2

Clinical Decision Algorithm

For infants less than 13 days old:

• Consider alternative antibiotics first: amoxicillin (classified as "compatible") or cephalosporins like cephalexin or ceftriaxone (also "compatible") if they are appropriate for the infection being treated 2
• If azithromycin is clinically necessary and no suitable alternative exists, use it but monitor the infant closely for signs of pyloric stenosis 2

For infants older than 2 weeks:

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

Infant Monitoring Requirements

• Monitor all breastfed infants for gastrointestinal effects including diarrhea or gastroenteritis, as systemic antibiotics in breast milk can alter intestinal flora 1, 3
• For infants under 13 days old exposed to azithromycin, watch specifically for signs of hypertrophic pyloric stenosis: projectile vomiting, poor feeding, and dehydration 2
• Be aware that antibiotics in breast milk could cause falsely negative cultures if the breastfed infant develops fever requiring evaluation 1, 3

Pharmacokinetic Considerations

• Research demonstrates that the median relative cumulative infant dose of azithromycin through breast milk is 15.7% of the maternal dose, which exceeds the recommended 10% safety limit 4
• Despite this higher transfer rate, the absolute infant dose remains low at approximately 4.5 mg/kg over 28 days postpartum 4
• Azithromycin is distributed into breast milk, though the concentrations are generally small and much less than therapeutic doses given directly to infants 1, 5

Common Pitfalls to Avoid

• Do not automatically discontinue breastfeeding when azithromycin is prescribed—the benefits of continued breastfeeding typically outweigh the minimal risks, especially after the first 2 weeks of infant life 3, 2
• Do not assume all macrolides carry identical risk profiles: clarithromycin shares the same pyloric stenosis risk during the first 13 days, while erythromycin is also classified as "probably safe" with similar timing considerations 1
• Do not rely on breast milk concentrations of azithromycin for therapeutic treatment of the infant—if the infant has an infection requiring treatment, they need their own appropriate therapeutic dosing 6

Preferred Alternatives When Clinically Appropriate

• Amoxicillin is classified as "compatible" with breastfeeding (the highest safety designation) and should be considered first-line for susceptible infections 1, 3
• Cephalosporins including cephalexin and ceftriaxone are also "compatible" with breastfeeding and represent excellent alternatives for appropriate indications 1, 3
• Amoxicillin/clavulanic acid is considered safe and effective during breastfeeding, classified as FDA Category B and explicitly compatible with nursing 1, 3