Azithromycin Use During Lactation
Azithromycin can be taken during lactation and is classified as "probably safe" by major guidelines, though breastfeeding infants should be monitored for gastrointestinal effects and, if exposed during the first 13 days of life, for signs of hypertrophic pyloric stenosis. 1
Safety Classification and Evidence
The European Respiratory Society/Thoracic Society of Australia and New Zealand (ERS/TSANZ) guidelines classify azithromycin as "probably safe" during breastfeeding, representing a high level of safety designation for antibiotics during lactation. 1
The FDA classifies azithromycin as Pregnancy Category B, and while the drug label states "it is not known whether azithromycin is excreted in human milk," it recommends caution when administered to nursing women. 2
Research confirms that azithromycin is indeed excreted into breast milk with sustained concentrations up to 48 hours after a single dose, and simulations demonstrate accumulation after multiple doses. 3
Clinical Decision Algorithm
Azithromycin is the preferred macrolide for infants under 1 month of age when maternal treatment is necessary, as it has not been associated with infantile hypertrophic pyloric stenosis (IHPS) unlike erythromycin. 4
For penicillin-allergic breastfeeding mothers requiring antibiotic therapy, azithromycin serves as a safe alternative to beta-lactam antibiotics. 1, 5
If amoxicillin/clavulanic acid is contraindicated or ineffective, azithromycin represents the next best choice with strong safety data. 1
Critical Monitoring Considerations
There is a very low risk of hypertrophic pyloric stenosis in infants exposed to macrolides during the first 13 days of breastfeeding, but this risk does not persist after 2 weeks. 1
All breastfed infants whose mothers take azithromycin should be monitored for gastrointestinal effects including diarrhea, loss of appetite, and altered intestinal flora. 1, 6
Parents should be counseled about signs of IHPS (projectile vomiting, dehydration) if azithromycin is used during the early postpartum period, though the absolute risk remains very low. 4, 7
Pharmacokinetic Data Supporting Safety
Research demonstrates that the median relative cumulative infant dose is 15.7% of the maternal dose (95% prediction interval: 2.0-27.8%), which exceeds the traditional 10% safety threshold but has not been associated with serious adverse events in clinical practice. 7
A prospective controlled study found that adverse reaction rates in infants exposed to macrolides (12.7%) were comparable to those exposed to amoxicillin (8.3%), with no cases of pyloric stenosis observed. 6
The most common minor adverse reactions reported were rash, diarrhea, loss of appetite, and somnolence—all self-limited and not requiring discontinuation of breastfeeding. 6
Important Caveats
Azithromycin should ideally be avoided during the first 13 days postpartum when the theoretical risk of IHPS is highest, though even during this period the absolute risk remains very low with a worst-case number needed to harm of 60. 1, 7
The small amounts of antibiotic in breast milk should not be considered therapeutic for the infant—if the baby develops an infection, they require their own appropriate dosing. 1
Antibiotics in breast milk could potentially cause falsely negative cultures if the breastfed infant develops fever requiring evaluation. 1, 5