The human head louse (Pediculus humanus capitis) is one of two obligate blood feeding lice on humans and along with its ecotype, the human body louse (Pediculus humanus humanus), have cause misery and death to countless millions. With the advent of antibiotics, the bacterial diseases vectored by body lice have been diminished but head louse infestations remain a persistent concern involving secondary infections and a variety of social issues for many. Since the 1980s, the control of head louse infestations has been largely achieved by applying two pediculicidal formulations; Nix® (1% permethrin) and Ovide® (0.5% malathion). Resistance to both products has now occurred resulting in a critical need for new and novel pediculicidal products. For the first time, there are currently three novel-acting, FDA-approved, pediculicides available by prescription (Sklice®, Natroba®, Xeglyze®) and one FDA-approved, OTC medical device (Nix ULTRA®). Sklice® is a single-use lotion with 0.5% ivermectin as the active ingredient and has recently (2020) been approved as an OTC product. Ivermectin is an agonist at the invertebrate glutamate-chloride channel. It is not directly ovicidal but acts as a post-eclosion nymphicide by blocking feeding. Natroba™ is a pediculicide for the topical treatment with 0.9 % spinosad (a 5:1 mixture of spinosyn A and spinosyn D) as the active ingredients. Spinosad is an agonist at the insect nicotinic acetylcholine receptor, causing nervous system excitation, involuntary muscle contractions, tremors and paralysis. Xeglyze® is a single-use lotion with 0.74 % abametapir as the active ingredient. Abametapir is a general metal chelator and acts as a metalloproteinase inhibitor, inhibiting processes critical in embryogenesis, egg hatching and louse survival. In addition to killing adults and nymphs, it is ovicidal under in vitro, ex vivo and in vivo conditions. Dimethicone-based medical devices for the treatment of head louse infestations (e.g., Nix ULTRA, LiceMD, NYDA) are dimethylsiloxane polymers, which have high surface spreading characteristics and act as suffocants on eggs and crawling lice. Recent regulatory, legal and production actions will be discussed in terms of how they have impacted effective and sustainable head louse control in the US.

New ligands for the control of human head lice, Pediculus humanus capitis

ACS Fall 2021

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