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 …