Pediculosis capitis - Emerging treatments

Permethrin 5%

In patients who do not respond to standard treatments, permethrin 5% may be used. It is 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%.[90][91] It is not commonly used in the US or in other countries. Permethrins are not recommended for use in the UK, as the formulations and licensed application methods of currently available products make them unsuitable for treating head lice. Additionally, there is evidence of resistance in the UK and other countries, further limiting their effectiveness.[30][92]

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 a 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.[93] 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.[94] Ivermectin is not licensed for this indication anywhere in the world.

Crotamiton

Available 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.[95] However, its true efficacy is not known. It is only available in some countries.

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.[96] 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 randomised 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%).[97] It is available in some countries but not currently in the US.