Evidence in the Treatment of Head Lice: Drowning in a Swamp of Reviews
- 1Department of Dermatology, Ghent University Hospital, Belgium
- 2Heymans Institute of Pharmacology, Ghent University, Belgium
- Reprints or correspondence: Dr. H. Lapeere, Dept. of Dermatology, University Hospital Ghent, De Pintelaan 185, 9000 Ghent, Belgium (hilde.lapeere{at}Ugent.be).
Sir—We read with interest the article by Jones and English [1] entitled “Review of Common Therapeutic Options in the United States for the Treatment of Pediculosis Capitis.” We would like to point out that there are currently no uniform guidelines on which a review of head lice treatment should be based, which has led to the publication of conflicting reviews in major medical journals, such as Lancet, New England Journal of Medicine, British Medical Journal, and Cochrane Database of Systematic Reviews (Cochrane Reviews) [2–6].
Two systematic reviews of the topical treatment of head lice with insecticides were published, one by Vander Stichele et al. [5] in 1995 and another in a Cochrane review by Dodd in 1999, which was later revised in 2001 [6]. The 2 reviews used different methodological approaches and had different results. We noticed that the current review by Jones and English [1] was based on the 1999 Cochrane review and that the earlier review by Vander Stichele et al. [5] was completely ignored.
The review by Vander Stichele et al. [5] identified 28 clinical trials, of which 7 met the inclusion criteria. They also identified 11 unpublished trials that compared the efficacies of permethrin and malathion [5]. Data from these trials were withheld by the manufacturer, thus causing an important publication bias.
The main conclusion in Vander Stichele et al. [5] was that there is only sufficient evidence available on the efficacy of permethrin and that evaluation of the efficacy of malathion and carbaryl requires more evidence. Lindane and natural pyrethrins were considered to have lacked sufficient efficacy [5].
The review by Jones and English [1] was based on the Cochrane review by Dodd [6], which was published in 1999 and revised in 2001. The objective of the Cochrane review was “to assess the effects of interventions in the treatment of head lice” [6]. Inclusion criteria for randomized controlled trails were the presence of live lice or “lice and eggs” (not just eggs alone) and the absence of treatment with any other pediculicide during the month preceding enrollment. An additional inclusion criterion was that lice and eggs should not be removed by combing after treatment with a pediculicide. The Cochrane review identified 71 trials, of which only 3 met the selection criteria—2 placebo-controlled trials by Taplin et al. [7, 8] and 1 comparative clinical field study by Burgess [9]. On the basis of the results of only 3 trials, the Cochrane review concluded that effectiveness was proven for permethrin, malathion, and synergized pyrethrins [6].
Many people who are working in this area are rather disappointed by the Cochrane review on head lice interventions [10]. Indeed, the 3 accepted trials were conducted in developing countries and involved populations who do not reflect infested patients in the United States or any other developed country, as was mentioned by Jones and English [1]. Furthermore, the definition of infestation that was used excluded several studies, because many researchers take it for granted that only patients with live lice or eggs are included in such studies. Every trial that did not explicitly mention this criterion was excluded, even if the inclusion of patients was properly done. The selection of trials and the assessment of quality can be heavily biased by personal communication. The Cochrane review also ignored 2 trials referenced in Vander Stichele et al. [5], and it still has not solved the publication bias mentioned above.
We also have remarks on the recommendation by Jones and English [1] to use formic acid to remove nits. This recommendation is based on a single study by DeFelice et al. [11], in which an “after-pediculicide nit removal system” (containing a formic acid cream rinse and a metal comb) was tested. Control and treated sites were combed with plastic and metal combs, respectively. The comb type alone (i.e., independent of the formic acid rinse) could account for the greater number of nits removed from the treated site.
Another important aspect in the treatment of head lice, which was not discussed in the review by Jones and English [1], concerns the bug-busting (i.e., wet-combing) method. The revised version of the Cochrane review states that bug busting is “ineffective” [6]. This conclusion is based on a trial by Roberts et al. [12]. In this pragmatic trial, the efficacy of bug busting was compared with that of malathion 0.5%. This study showed a cure rate of 78% for malathion and 38% for the bug-busting method. The authors jumped to the conclusion that “policies advocating bug-busting as first-line treatment for head lice infestations are inappropriate for the general population” [12, p. 543]. This conclusion is found repeatedly in new reviews on head lice treatments [4, 6]. However, until now, only 1 small efficacy trial with insufficient power, in which the efficacy of bug busting was compared with that of phenothrin lotion, has been performed [13]. Larger efficacy trials should yield valuable information. Conclusions about bug busting should not be based on the results of a pragmatic study, because every kind of treatment—chemical, as well as bug busting—can lead to bad results in a pragmatic study [14].
Other comments on the trial by Roberts et al. [12] are that its outcome depended on local resistance patterns to malathion. In regions where head lice are highly resistant to malathion, bug busting could perform better than the chemical treatment. Additional advantages of bug busting that were not taken into account include its low cost and the fact that it can be repeated over and over again without any side effects [15–17].
The bug-busting method cannot be written off because it was shown to be less effective than a chemical method in a pragmatic trial. An efficacy trial with sufficient power should be done first to determine the actual therapeutic value of bug busting.
We are also concerned about the way ivermectin is almost “promoted” as a quick fix for treating head lice in the review by Jones and English [1]. The reviewers should have adopted a more critical attitude toward the use of ivermectin for treating head lice. Head lice are still no official indication for the use of ivermectin, and nothing is known about the long-term effects of ivermectin in the battle against head lice.
The controversy on the interpretation of research on head lice treatment was discussed during the 2nd International Congress on Phthiraptera (Brisbane, Australia) in July 2002, but, unfortunately, no criteria for conducting quality trials and performing systematic reviews were formulated. Although the debate is ignored in scientific literature, the need for a uniform reference standard on the basis of which reviews on the treatment of head lice can be conducted still stands.
It is our opinion that a review should be a critical analysis of all available information. All evidence should be taken into account, including that from published and unpublished trials. It is high time for an international group of experts to define a set of criteria that can be used to evaluate results of clinical trials before they are included in a review. A high-quality review on head lice treatment is what many practitioners need, instead of the current swamp of reviews of disputable quality.
- © 2003 by the Infectious Diseases Society of America
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