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Oral Ivermectin is more effective than topical malathion in difficult-to-treat head lice infestation

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Study design

Design Randomised controlled trial.

Allocation Stratified block randomisation of clusters. Treatment allocation was concealed.

Blinding Double-blind.

Setting Clinical research sites and hospital departments in the UK, Ireland, France and Israel.

Patients The inclusion criteria comprised: aged 2 years or older, weight 15 kg or greater and a history of failure of previous head lice treatment (defined as persistence of head lice despite topical application of a pyrethroid- or malathion-based insecticide 2–6 weeks before recruitment).

Intervention 812 participants (in 376 households) were randomised to receive either oral Ivermectin (Stromectol, 400 μg/kg) on days 1 and 8, or 0.5% alcoholic malathion lotion (Prioderm). Within each participating household (cluster), all infested members were allocated to the same treatment. A double-dummy technique was used to maintain blinding. The lotions (malathion or placebo) were applied by an investigator on days 1 and 8. Participants were not permitted to have other pediculocidal treatments during the study period, and were asked not to share fomites and avoid head-to-head contact with others. Patients who still had head lice infestation on day 15 were switched to the …

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  • Sources of funding The manufacturer of Ivermectin (Johnson & Johnson–Merck Sharp & Dohme-Chibret) funded the trial, was involved in the study design and provided the study medications. A ‘contract research organisation’ collected the data. An industry author was involved in the writing of the manuscript. All but one author received consulting fees from the manufacturer, held stock options in the company or were employed by the manufacturer.


  • Competing interests None.

  • Provenance and peer review Commissioned, internally peer reviewed.