TERBINAFINE

Fetal Risk Summary

Terbinafine is a synthetic allylamine antifungal agent that is indicated for the treatment of onychomycosis of the toenail or fingernail due to dermatophytes (tinea unguium) (1). No studies evaluating the placental transfer of terbinafine in humans have been located. The molecular weight (about 328) is low enough that transfer to the fetus should be expected.

Reproduction studies have been conducted in rats and rabbits (1). Oral doses in rats up to approximately 12 times the maximum recommended human dose based on body surface area (MRHD) had no effect on fertility or other reproductive parameters. In pregnant rabbits, intravaginal administration of terbinafine did not cause abortions, premature delivery, or affect fetal parameters. In pregnant rats and rabbits, no evidence of impaired fertility or fetal harm was seen with oral doses up to 12 and 9 times the MRHD, respectively (1).

Although the animal reproduction data are encouraging, the lack of human pregnancy data do not allow a full assessment of the fetal risk from terbinafine. If possible, therefore, waiting to begin treatment until after a pregnancy has been concluded would be the safest course.

Breast Feeding Summary

Terbinafine is excreted into human milk (1). No specific details were given, but the milk:plasma ratio in nursing women was 7:1. The effects of this exposure on a nursing infant are unknown. Because the duration of therapy is usually prolonged (6 or 12 weeks for patients with fingernail or toenail onychomycosis, respectively), the potential for serious toxicity in a nursing infant may be increased. Based on the accumulation in milk and the prolonged exposure, women taking terbinafine should probably not breast feed.

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