Percutaneous absorption of malathion is limited. In vitro studies in isolated skin suggest the percutaneous absorption of malathion from a topically applied aqueous ethanolic solution to be approximately 10% (4). Similarly in a study of human volunteers, approximately 4% of the dose applied to the skin was absorbed and this proportion did not change with repeated daily application to the same site for 8 days (5). Malathion is hydrolysed and detoxified by plasma carboxylesterases much more rapidly in man than in insects, giving rise to selective toxicity and a low potential for toxicity in man (6,7). A small, open study investigated the safety of four malathion head lice preparations by applying a dose to the scalp and measuring any effects on plasma and erythrocyte cholinesterase. None of the preparations has any clinical effect on either plasma or erythrocyte cholinesterase activity irrespective of single or repeat dose treatment, or whether applied to damaged or intact skin (8). Permethrin Lyclear ® Dermal Cream (permethrin 5%) is licensed for the treatment of pubic lice. The SPC for Lyclear ® Dermal Cream (Omega Pharma) states that studies, following oral administration of permethrin in cattle have indicated that very low concentrations of permethrin are excreted in milk. It is not known whether permethrin is excreted in human breast milk. However, because only extremely small amounts of permethrin are absorbed systemically following treatment with Lyclear ® Dermal Available through NICE Evidence Search at 1
Medicines Q&As Cream, and in theory only a very small percentage of this systemic permethrin may pass into the breast milk, it is unlikely that the concentrations of permethrin in the milk will present any risk to the neonate/infant (9). Hale notes that permethrin absorption through the skin following application of a 5% cream is reported to be less than 2%. Permethrin is rapidly metabolized by serum and tissue enzymes to inactive metabolites and rapidly excreted in the urine. Overt toxicity is very low. The WHO considers short- term topical use of permethrin as compatible with breastfeeding (7).
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- Fall '19
- Head louse, Breast milk, Lactation, Crab louse, permethrin