Is fosfomycin (antibiotic) safe during breastfeeding?

Fosfomycin Safety During Breastfeeding

Fosfomycin can be used during breastfeeding with caution, though data are limited; the decision should weigh maternal benefit against unknown infant risk, as excretion into breast milk is not well-characterized.

Key Safety Considerations

Limited Human Data

• It is not known whether fosfomycin is excreted in human milk, according to FDA labeling 1
• The FDA recommends that a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the medication to the mother 1
• No published pharmacokinetic studies document fosfomycin concentrations in breast milk or infant exposure levels 1

Theoretical Safety Profile

• Fosfomycin has low oral bioavailability, which suggests minimal systemic absorption by the nursing infant even if present in breast milk 1
• The drug is administered as a single-dose treatment (3 grams once), limiting the duration of potential infant exposure 1, 2
• Most antibiotics used for urinary tract infections are considered relatively safe during breastfeeding when infant exposure through breast milk is minimal 3, 4

Clinical Decision Algorithm

When Fosfomycin May Be Reasonable

• Maternal urinary tract infection requires treatment and fosfomycin is clinically indicated 2
• Safer alternatives with established breastfeeding safety data (such as amoxicillin, cephalexin, or nitrofurantoin) are contraindicated or have failed 5, 6
• The infant is full-term, healthy, and can be monitored for adverse effects 5

Preferred Alternatives with Better Safety Data

• First-line options: Amoxicillin or cephalosporins (cephalexin, cefuroxime) are considered compatible with breastfeeding 7, 5, 6
• Second-line options: Azithromycin (probably safe, avoid first 13 days due to very low pyloric stenosis risk) 7, 5
• Third-line options: Ciprofloxacin if benefits outweigh theoretical cartilage damage risks 6

Monitoring Recommendations

Infant Surveillance

• Monitor for gastrointestinal effects including diarrhea, as most systemic antibiotics alter intestinal flora 7, 5
• Watch for signs of antibiotic-associated complications such as candidiasis or feeding difficulties 8, 4
• Be aware that antibiotics in breast milk could cause falsely negative cultures if the infant develops fever requiring evaluation 5, 6

Timing Considerations

• If fosfomycin is used, consider timing the single dose immediately after breastfeeding to minimize infant exposure at peak maternal serum concentrations 8
• The single-dose regimen (versus multi-day courses) inherently limits exposure duration 1, 2

Common Pitfalls to Avoid

• Do not assume pregnancy safety equals breastfeeding safety: A drug safe during pregnancy may not be safe for the nursing infant 8
• Avoid unnecessary discontinuation of breastfeeding when safer antibiotic alternatives with established lactation data exist 5, 4
• Do not use fosfomycin as first-line when better-studied antibiotics are appropriate for the clinical indication 5, 6