Is azithromycin (Z‑Pack) safe for a breastfeeding mother and her newborn?

Azithromycin (Z-Pack) Safety During Breastfeeding for Newborns

Azithromycin is classified as "probably safe" during breastfeeding and can be used by nursing mothers, but it should ideally be avoided during the first 13 days postpartum due to a very low risk of infantile hypertrophic pyloric stenosis (IHPS). 1, 2

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 the second-highest safety designation for antibiotics in lactation. 1, 2

• The critical timing window is the first 13 days postpartum: An epidemiological study identified 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, 2

• After 2 weeks postpartum, azithromycin can be used safely without the IHPS concern. 1, 2

FDA Drug Label Information

• The FDA label states that it is not known whether azithromycin is excreted in human milk, and caution should be exercised when administering to nursing women. 3

• Azithromycin is classified as Pregnancy Category B, indicating animal studies showed no harm, though human data during lactation remain limited. 3

Infant Exposure and Monitoring

• Research shows that the median cumulative infant dose through breast milk is approximately 15.7% of the maternal dose (range 2.0-27.8%), which exceeds the traditional 10% safety threshold used in lactation pharmacology. 4

• Despite this higher-than-typical transfer rate, serious adverse effects in breastfed infants are rare. 2

• Parents should be counseled to watch for signs of IHPS if azithromycin is used in the early postpartum period, including projectile vomiting and dehydration, though the absolute risk remains very low. 2

• All breastfed infants should be monitored for gastrointestinal effects such as diarrhea or gastroenteritis due to alteration of intestinal flora. 1, 2

Clinical Decision Algorithm

1. Determine the infant's age: If the newborn is less than 13 days old, consider safer alternatives first (see below). 1, 2

2. If azithromycin is necessary in the first 13 days: Use only when benefits clearly outweigh risks, counsel parents about IHPS warning signs, and consider closer monitoring. 1, 2

3. After 13 days postpartum: Azithromycin can be used with standard precautions for antibiotic use during breastfeeding. 1, 2

4. Monitor the infant for feeding changes, vomiting, irritability, or diarrhea during maternal treatment. 2

Safer First-Line Alternatives

If treating a breastfeeding mother with a newborn under 13 days old, consider these fully compatible alternatives:

• Amoxicillin or amoxicillin/clavulanate (Augmentin) are classified as "compatible" with breastfeeding and represent the safest first-line choice. 1, 2, 5

• Cephalosporins (such as cephalexin or ceftriaxone) are also classified as "compatible" and are excellent alternatives. 1, 2, 5

• Erythromycin is suggested as safe for penicillin-allergic patients, though it carries the same theoretical IHPS risk as azithromycin in the early postpartum period. 1

Common Pitfalls to Avoid

• Do not unnecessarily discontinue breastfeeding when azithromycin is prescribed after the first 2 weeks postpartum, as the benefits of continued breastfeeding outweigh the minimal risks. 6, 7

• Do not use azithromycin as a first-line agent in the first 13 days postpartum when safer alternatives like amoxicillin are available and appropriate for the infection being treated. 1, 2

• Do not forget to counsel parents about the warning signs of IHPS if azithromycin must be used in early infancy. 2

• Remember that antibiotics in breast milk may cause falsely negative bacterial cultures if the infant develops fever and requires evaluation. 2