Ivermectin for Head Lice

Abstract and Commentary

By Hal B. Jenson, MD, FAAP, Professor of Pediatrics, Tufts University School of Medicine, and Chief Academic Officer, Baystate Medical Center, Springfield, MA, is Associate Editor for Infectious Disease Alert.

Dr. Jenson reports no financial relationships relevant to this field of study.

Synopsis: For difficult-to-treat head lice infestation, oral ivermectin had superior efficacy to topical 0.5% malathion lotion, with no significant differences in adverse events.

Source: Chosidow O, et al. Oral ivermectin versus malathion lotion for difficult-to-treat head lice. N Engl J Med. 2010;362:896-905.

A multicenter, cluster (household)-randomized, double-blind, double-dummy, controlled trial was conducted in 812 patients (≥ 15 kg, and ≥ 2 years of age) from 376 households at seven study centers in the United Kingdom, Ireland, France, and Israel. Patients with head lice (determined by the presence of live lice with a standardized fine-toothed combing procedure) were randomized by household to prevent contamination between treatment groups, to receive on days 1 and 8 either oral ivermectin (400 mcg per kilogram, in 3-mg tablets) or 0.5% alcoholic malathion lotion, administered by staff on site. A double-dummy technique was used (placebo tablet or placebo lotion) to ensure that treatment remained blinded. Lotion was applied until all hair and scalp were thoroughly moistened, and allowed to dry naturally with instructions to leave the lotion in place for 10-12 hours and then to wash the hair with mild shampoo, which was provided. No other pediculicidal treatments were permitted. The primary endpoint was absence of live head lice on day 15, determined by repeat combing procedure. Patients with persistent head lice infestation on day 15 were switched to the other treatment at the same dose.

The ivermectin group consisted of 398 patients in 185 households, and the malathion group consisted of 414 patients in 191 households. The two groups were comparable with regard to household characteristics. The study population was predominantly female (86.9%), with a median age of 10 years (interquartile range, 7 to 14 years) and median weight (± SD) of 40 ± 22 kg. Approximately 15% of households had more than three family members with head lice infestation. On day 15, 35 patients (4.3%) were lost to follow-up, and 53 patients (6.5%) did not complete the study.

In the intention-to-treat population, 95.2% of patients receiving ivermectin were free of lice on day 15, compared to 85.0% of patients receiving malathion (absolute difference of 10.2%; 95% CI, 4.6-15.7%; p < 0.001). In the per-protocol population, 97.1% of patients in the ivermectin group were free of lice on day 15, compared to 89.8% of patients receiving malathion (absolute difference of 7.3%; 95% CI, 2.8-11.8%; p = 0.002). There were no significant differences in the frequency of adverse events between the two treatment groups.


Head lice infest more than 100 million individuals worldwide each year, with children 3 to 10 years of age most likely to be affected. Emerging pyrethroid resistance has led to the reintroduction of malathion as an effective alternative treatment. This trial showed the noninferiority and superiority of oral ivermectin (400 mcg per kilogram) to 0.5% malathion lotion, each given on days 1 and 8, for eradicating head lice infestation. Important principles of head-lice treatments include a second dose no earlier than 7 days and no more than 11 days after the first dose in order to kill head lice that hatch from eggs surviving the first treatment, and concomitant treatment of all infested family members.

In this study, more households were free of lice after oral ivermectin than after malathion lotion, suggesting that ivermectin might be more effective in controlling infestations among close contacts, such as in the classroom setting. Ivermectin has been used to treat onchocerciasis since 1987, with recent evidence of genetic selection for ivermectin-resistant Onchocerca volvulus. Concern about development of resistant head lice suggests that ivermectin should be considered only for patients with persistent head-lice infestation after failure of topical treatment. Ivermectin is not recommended for children < 15 kg, pregnant women, or mothers who are breast-feeding.