No reports describing the use of topical permethrin during lactation have been located. Although the molecular weight (about 391) is low enough for excretion into breast milk, the minimal systemic absorption and rapid metabolism suggest that little, if any, of the drug will be found in milk. The CDC considers permethrin or pyrethrins with piperonyl butoxide to be the treatment of choice for pubic lice during lactation. For infants, pregnant, and lactating women with scabies, permethrin is considered the treatment of choice in the United States and Europe (1,2).

Permethrin, a pyrethroid, is indicated for the topical treatment of Sarcoptes scabiei (scabies) infestations. The drug is also active against lice, ticks, fleas, mites, and other arthropods. In patients with moderate to severe scabies, systemic absorption was estimated to be ≤2% of the dose (3).

Animal Data: Oral reproduction studies with permethrin have been conducted in mice, rats, and rabbits at doses of 200-400 mg/kg/day (3). No adverse effects on fertility or evidence of fetal harm were observed in these studies. Species-specific carcinogenesis was observed in mouse studies but negative results were seen in rats. Genetic toxic studies revealed no evidence of mutagenicity (3). Only the highest oral concentrations (2500-4000 ppm) of permethrin administered after implantation were found to lower significantly the protein and glycogen contents of rat placentas, but this had no statistical effect on the number of live fetuses (4).

Placental Transfer: Although no studies of permethrin placental transfer have been located, the molecular weight (about 391) is low enough that transfer should occur. However, because only small amounts are absorbed systemically and these are rapidly metabolized by ester hydrolysis to inactive metabolites, the opportunity for fetal exposure to permethrin appears to be minimal, if it occurs at all.

Human Data: A 1995 case report described the use of multiple courses of permethrin and other agents in a pregnant woman who had developed crusted scabies (6). She was initially treated at 2 months with monosulfiram (a pesticide not available in the United States). Relapse occurred at 5 months, and she was treated with two total-body (24-hour) applications of malathion 0.5% liquid and one total-body (24-hour) application of monosulfiram 25% solution. Three weeks later another relapse occurred, and she was treated with permethrin 5% cream to the whole body for 12 hours. Because live mites were found the next day, a sulfur/tar/coconut oil soak to the scalp was used 3 times daily followed by two total-body benzyl benzoate 25% treatments within 24 hours. Then permethrin cream was used weekly for 3 weeks. A healthy male infant was delivered at term (5).

A 2005 observational study compared 113 pregnancies exposed to permethrin sometime in gestation with 113 matched controls (6). There were no differences between the groups in pregnancy outcomes in terms of live births, spontaneous abortions, therapeutic abortions, major malformations, birth weight, and gestational age at delivery.