Oral Terbinafine During Breastfeeding
Oral terbinafine is not recommended while breastfeeding due to high milk-to-plasma concentration ratios and lack of safety data in nursing infants.
FDA Drug Label Guidance
The FDA drug label explicitly states that "treatment with terbinafine is not recommended in nursing mothers" 1. This recommendation is based on pharmacokinetic data showing that after oral administration, terbinafine is present in breast milk with a milk-to-plasma ratio of 7:1 1. This means the infant would be exposed to concentrations seven times higher than maternal plasma levels through breast milk.
Key Pharmacologic Concerns
The high milk concentration is particularly concerning because:
- Terbinafine is highly lipophilic and distributes extensively into tissues, with a terminal half-life of 200-400 hours representing slow elimination from tissues 1
- >99% protein binding in plasma, but the unbound fraction in milk could still expose the infant to significant amounts 1
- The drug persists in tissues for months after treatment completion (detectable for 6 months post-therapy) 2
Clinical Decision-Making Algorithm
When a breastfeeding mother requires antifungal treatment:
For onychomycosis (nail fungus): Treatment can be safely postponed until after breastfeeding is complete, as this is not a life-threatening condition 1
For dermatophyte infections requiring systemic therapy: Consider griseofulvin as an alternative, which is the only oral antifungal licensed for use in children as young as 1 month 2, suggesting a better safety profile for infant exposure
For localized fungal infections: Use topical antifungals (amorolfine, ciclopirox) instead, which have minimal systemic absorption 2
Important Caveats
- No published studies have evaluated infant outcomes after maternal terbinafine use during lactation
- The 7:1 milk-to-plasma ratio means even "low" maternal doses result in substantial infant exposure
- Unlike pregnancy data (where no increased risk of malformations was found 3), there are no comparable safety data for lactation
- The drug's long tissue half-life means it cannot be "timed" around feedings to reduce infant exposure
The recommendation is clear: avoid oral terbinafine while breastfeeding and use alternative treatments or delay therapy until after weaning.