Pediculosis capitis - Emerging treatments

Permethrin 5%

In patients who do not respond to standard treatments, permethrin 5% may be used. It is only available as a cream for scabies and pubic pediculosis, but has been recommended for the treatment of head lice that appear to be recalcitrant to other treatments. One study suggested that lice resistant to treatment with permethrin and other compounds with a neurotoxic mode of action in a normal dose will not succumb to higher concentrations of the chemical. The risk for toxic adverse events is higher than with permethrin 1%.[80][81] It is not commonly used in the US or in other countries.

Isopropyl myristate/cyclomethicone

Should not be used in children younger than 4 years old. It is a hair rinse that dissolves the waxy exoskeleton of the louse, leading to dehydration and death. It is not ovicidal. The evidence of efficacy is not strong enough to recommend it, except in special circumstances (such as possible resistance to other pediculicides).[82][83] It is available in some regions such as Canada, Australia, and Europe, and is a common treatment option in these countries.

Oral ivermectin

A single dose, repeated in 10 days, has been shown to be effective against head lice if sufficient concentration is present in the blood at the time a louse feeds. For difficult-to-treat head-lice infestation, oral ivermectin, given twice with a 7-day interval, had superior efficacy as compared with topical 0.5% malathion lotion, a finding that suggests that ivermectin could be an alternative treatment.[84] If ivermectin gets across the blood-brain barrier, it blocks essential neural transmission; young children may be at higher risk for this adverse drug reaction. Therefore, ivermectin should not be used for children who weigh less than 15 kg and are younger than 5 years old. However, one study reported one seizure in the ivermectin group even with children >15 kg.[85] Ivermectin is not licensed for this indication anywhere in the world.

Crotamiton

Available by prescription as a lotion used to treat scabies. A single study showed it to be effective against head lice when applied to the scalp and left on for 24 hours before rinsing out.[86] However, its true efficacy is not known. It is only available in some countries.

Dimethicones

Dimethicones belong to the group of synthetic silicone oils. The chain length and the solvent determine the viscosity of the product and other physical properties.[87] Dimethicones with low surface tension can perfectly coat microscopic surfaces. They have a purely physical mode of action. If applied on a louse, they coat the cuticle of the insect, enter into the spiracles (tiny tracheae-like tubes leading into the louse body), and displace the air needed for breathing. They may also disrupt water management and cause subsequent osmotic stress and probable rupture of the gut. This causes death of the parasite with a delay of several hours.[88][89] A 4% dimeticone solution in cyclomethicone showed an efficacy rate of between 70% and 92%.[90][91][92] Another mixture of two dimethicones showed an efficacy rate of 97% in a population with a high intensity of infestation in Brazil.[93] In randomized control trials, dimethicones performed significantly better than permethrin 1% and malathion.[90][93][94] Some products also show high efficacy against eggs; however, there are no randomized controlled trials to support this.[95][96][97] Dimethicones are colorless and odorless and are considered nontoxic. Because of their mode of action, the development of resistance in lice is very unlikely. A systematic review concluded that dimethicones should be considered as the first-line treatment.[98] Dimethicones are not currently available in the US, but are used as a main treatment option in many countries in Europe, including the UK.

1,2-octanediol

A surfactant that can be applied as a lotion or an alcohol-free mousse. 1,2-octanediol has been found to eliminate head louse infestation. It is thought to disrupt the insect's cuticular lipid, resulting in dehydration. The alcohol-free mousse has been shown to result in significantly fewer adverse reactions than the lotion.[99] It is only available in some countries.

Tocopheryl acetate

Tocopheryl acetate is a viscous, oily fluid used in some skin and scalp care products. In one randomized trial that enrolled 45 people, a tocopheryl acetate 20% spray preparation was found to be more effective at eliminating head lice than permethrin 1% (57% vs 23%).[100] Available in some countries but not currently in the US.