Is nitrofurantoin safe to use during lactation?

Nitrofurantoin Safety During Lactation

Nitrofurantoin is generally safe to use during lactation, but caution is warranted in mothers nursing infants younger than 1 month due to theoretical concerns about hemolytic anemia risk, particularly in infants with glucose-6-phosphate dehydrogenase deficiency.

Mechanism and Transfer into Breast Milk

• Nitrofurantoin is actively transported into human milk, achieving concentrations in milk that exceed those in maternal serum 1
• Studies show milk-to-serum concentration ratios of approximately 2.2-6.2 2, 1
• Despite this active transport, the absolute amount transferred to the infant remains relatively small:
  • Only 0.05-0.28% of the maternal dose is excreted in breast milk 2
  • Estimated infant exposure is approximately 0.2 mg/kg/day or about 6% of the weight-adjusted maternal dose 1

Safety Considerations

General Safety

• The 2020 American College of Rheumatology guidelines conditionally recommend nitrofurantoin as compatible with breastfeeding 3
• Most clinical guidelines consider nitrofurantoin a first-line agent for uncomplicated UTIs, including in lactating women 4

Special Considerations for Young Infants

• Theoretical concern exists for hemolytic anemia in newborns under 1 month of age due to:
  • Glutathione instability in very young infants
  • Potential risk in infants with glucose-6-phosphate dehydrogenase deficiency 5
• Some experts suggest glutathione stability may be established by the eighth day of life, reducing this risk in older neonates 5

Recommendations for Clinical Practice

For Mothers Nursing Infants Older Than 1 Month

• Nitrofurantoin can be safely used as a first-line agent for uncomplicated UTIs
• Standard dosing regimens (100 mg twice daily for 5 days) are appropriate 4
• No special monitoring of the infant is required

For Mothers Nursing Infants Younger Than 1 Month

• Consider alternative antibiotics as first-line therapy if equally effective options exist
• If alternatives are not suitable or available:
  • Nitrofurantoin can still be used with appropriate monitoring
  • The infant should be monitored by a physician for signs of hemolytic anemia (jaundice, pallor, irritability)
  • The benefits of continued breastfeeding generally outweigh the theoretical risks 5

Alternative Antibiotics During Lactation

If concerns exist about using nitrofurantoin in mothers nursing very young infants, consider:

• Trimethoprim-sulfamethoxazole (if local resistance <20%)
• Fosfomycin (3g single dose)
• Beta-lactams (though they have inferior efficacy for UTIs) 4

Important Caveats

• Nitrofurantoin is contraindicated in patients with renal impairment of any degree 6
• Rare but serious adverse effects can occur in the mother, including pulmonary reactions and systemic inflammatory response syndrome 6, 7
• The decision to use nitrofurantoin during lactation should balance the need for effective UTI treatment with the infant's age and risk factors