Patient's preferences and shared decision-making: Considering environmental aspects in head lice treatment

One of the most commonly used drugs to treat head lice is permethrin. This drug is also frequently used in veterinary medicine as a pet parasiticide, while its use as a plant protection agent is now restricted because of its ecotoxicity. This substance has been included as a priority substance in the proposal of the European Water Framework Directive and consequently, Environmental Quality Standard (EQS) have been established. Available literature shows that domestic treatment of head lice seems to be the main source of permethrin to municipal wastewater treatment plants (WWTP), while washing pet's hair could also be a contributing factor. Concentration in WWTP effluents are frequently > EQS for different environmental matrices. Besides, studies have shown very high concentrations in sludge, which is worrying considering its use as a fertilizer in agri-culture. The development of resistance of lice to permethrin has driven the development of drugs with different mode of action, such as dimethicone. This drug has shown comparable efficacy to permethrin without its environmental consequences. Moreover, non-pharmacological methods should be preferred when possible. As awareness about the environmental impact of medicines grows, these aspects may become a crucial part of patient's preferences in shared decision-making. Although the ecotoxicological impact of pharmaceuticals is still rarely considered by healthcare professionals or patients when using drugs, the One Health philosophy could also be applied when it comes to treating head lice. We can no longer consider a rational use of medicines if we continue to neglect their environmental impacts.