Oral Ivermectin: An Effective Alternative for the Treatment of Head Louse Infestation

Tamar F. Barlam, MD; Dennis L. Kasper, MD


AccessMedicine from McGraw-Hill 

Head lice affect more than 100 million people worldwide annually. Permethrin (1% formulation) is efficacious but resistance is emerging. Malathion (0.5% formulation) is an alternative, but resistance to this agent has likewise emerged. Ivermectin is effective against other parasites, but in a noncontrolled study, a single standard dose eradicated head lice in only 23% of subjects. Examining efficacy and safety, Chosidow and colleagues (2010) compared oral ivermectin at an increased dose of 400 mg/kg with malathion (0.5%) lotion in patients with difficult-to-eradicate head louse infestations.

A cluster-randomized, double-blind, double-dummy, controlled trial was conducted from March through September 2004 at seven sites in the United Kingdom, France, and Israel. Households were defined as clusters; once an index case was assigned a treatment, the entire household was enrolled in the same treatment group. The study had two stages: the primary stage and an extension stage for patients who still had louse infestation at day 15. Patients in the extension stage were switched to the other treatment arm in a double-blind crossover manner. Eligible patients included persons at least 2 years of age with head louse infestation against which treatment with either pyrethrin or malathion 2–6 weeks before enrollment had failed. All members of a household infested at the day 1 visit were eligible. No more than six household members were enrolled. On days 1 and 8, patients received either oral ivermectin or 0.5% malathion lotion and the corresponding placebo tablets or lotion. On day 15, participants with persistent infestation were switched to the alternative treatment. The primary endpoint was absence of live head lice on day 15; secondary outcomes were absence of live head lice on days 2 and 8 and—for patients in the extension stage—on days 22 and 29.

Overall, 376 households with 812 patients were enrolled. There were 398 patients from 185 households in the ivermectin group and 414 patients from 191 households in the malathion group. The households were well matched by severity of infestation. Most subjects were female (86.9%), with a median age of 10 years. On day 15 in the intention-to-treat analysis, 378 (95.2%) of 397 patients were free of head lice in the ivermectin group, as were 352 (85.0%) of 414 patients in the malathion group (absolute difference, 10.2%; 95% confidence interval, 4.6–15.7; p < .001). Examination by cluster showed that 171 (92.4%) of 185 households in the ivermectin group and 151 (79.1%) of 191 households in the malathion group were free of head lice at day 15. On day 15, 8 patients in the ivermectin group and 31 patients in the malathion group had persistent infestation. All patients but one were free of head lice by day 29. Patients preferred tablets to lotion (78.3% vs 13.0%). Adverse events were similar in the two groups.

Oral ivermectin appears to be highly effective for the treatment of head louse infestations and offers a good therapeutic alternative. Because its overuse may result in resistance, oral ivermectin should be reserved at this point for difficult-to-treat cases.


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