Oral Ivermectin for the Treatment of Pediculosis Capitis

Abstract

To the Editors: We read with interest the recent paper entitled “Oral ivermectin for treatment of pediculosis capitis” by Ameen et al.1 We believe that several aspects related to this publication require clarification. The authors' statement that “viable nits are opalescent white, ... nonviable nits are empty nit cases that are almost clear” is not entirely correct. Viable eggs are usually tan to brown in color, while nonviable eggs are white, opaque, or transparent.2,3 Also, technically, “nits” are hatched eggs, although the term is frequently erroneously used to describe viable eggs as in this instance. Importantly, most experts agree that the distinction between viable and nonviable eggs is difficult on visual inspection alone.4 Therefore, use of “viable” versus “nonviable nits” based on inspection as one of the primary outcomes in this study questions the reported findings. Unfortunately, the authors have also not detailed the method used to assess the presence of adult head lice. This is important, as published data show that the systematic use of a detection comb is far more effective than visual inspection alone.5 It is unclear why the authors did not include a control group in the study. While the use of a placebo is generally considered unethical in this setting, a control group treated with a conventional topical pediculicide is frequently used in studies investigating treatment efficacy in head lice infestation. The authors state that “there is only one study of systemic ivermectin [for the treatment of head lice] in the English literature,” referring to the paper by Glaziou et al.6 This overlooks the publication by Chosidow et al in the New England Journal of Medicine in January 2010,7 which generated much debate,8 as well as a paper by Pilger et al published the following month.9 Furthermore, a study investigating the efficacy of combinations of antiparasitic drugs for the treatment of head lice infestation published in 2009, also included oral ivermectin.10 Based on the collective published evidence, there is little doubt that ivermectin, a member of the avermectin class of insecticides, is effective for the treatment of head lice infestation. However, we believe that readers should be cautious about the use of this drug as a first-line agent. Although Ameen et al state that their data supports the “tolerability of ivermectin,” data from 44 children are insufficient to provide meaningful conclusions about the safety of this drug. Ameen et al state that the “safety [of ivermectin] has been demonstrated for more than a decade in its use in the control of onchocerciasis.” However, ivermectin treatment for onchocerciasis in patients with coexisting Loa loa microfilaremia has been reported to be associated with severe neurologic complications, including headaches, abnormal tendon reflexes, seizures, encephalopathy, and coma.11–13 While it is assumed that these complications are caused by the microfilarial organisms, the underlying pathologic mechanism remains unknown, and there is no certainty as to whether the drug itself plays a significant role. Notably, avermectin poisoning is well documented to result in prominent neurologic features, including abnormal tendon reflexes and coma.14 In addition, there are concerning data suggesting that the use of ivermectin in elderly patients may be associated with an increase in mortality, although again the causality remains unclear in this context.15 It would seem inappropriate to use a systemic treatment with the risk of potentially serious side effects, even if these are very rare, for a condition that is associated with no mortality and no long-term morbidity. While there is good evidence that conventional neurotoxic topical pediculicides (ie, malathion, permethrin, and pyrethrin) have become less effective as a result of the emergence of complex resistance mechanisms in the parasite population, newer, non-neurotoxic topical pediculicides have recently become available. Some of these agents, including dimethicone, which is also used in the treatment of infant colic, have been shown to have high efficacy in randomized controlled trials, and have excellent safety profiles.16 In addition, wet combing (ie, the physical removal of head lice), an intervention free from potential side effects, has been shown to be effective in a large proportion of patients in several studies.17 On the basis that there are several proven safe and effective alternatives to systemic treatment, we believe that physicians should not resort to using oral ivermectin for the routine treatment of head lice infestation, a sentiment that appears to be shared by Ameen et al. Marc Tebruegge, DTM&H DLSHTM, MRCPCH, MSc, MD Department of Paediatrics The University of Melbourne; Infectious Diseases Unit Department of General Medicine; Murdoch Children's Research Institute Royal Children's Hospital Melbourne Anastasia Pantazidou, MD Infectious Diseases Unit Department of General Medicine Royal Children's Hospital Melbourne Nigel Curtis, FRCPCH, PhD Department of Paediatrics The University of Melbourne; Infectious Diseases Unit Department of General Medicine; Murdoch Children's Research Institute Royal Children's Hospital Melbourne Parkville, Australia