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Head lice pharmacotherapy update for school year 2012-2013
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For the past several years, this column has reviewed and updated the treatment of one of the most common disorders affecting US children: Pediculus capitis, otherwise known as head lice. This review has been published in late summer to coincide with the start of the new school year, as transmission and infestation with head lice increase when school begins.
Last year saw the addition of a new FDA-labeled product, spinosad (Natroba, ParaPRO/Pernix Therapeutics), and this year adds another product — topical ivermectin 0.5% (Sklice Lotion, Sanofi-Pasteur). Pediatric clinicians can now choose from four relatively new prescription topical products that are labeled for use in infants and children by the FDA to treat head lice infestation: 1) malathion 0.5% (Ovide, Taro Pharma); 2) benzyl alcohol 5% (Ulesfia, Shionogi); 3) spinosad 0.9%; and 4) ivermectin 0.5%.
Edward A. Bell
This list does not include another FDA-labeled product that has been available for many years, lindane 1%. Lindane is no longer recommended by the AAP and other experts because of concerns over its safety and lack of efficacy. Several products available over-the-counter continue to be recommended for treatment of head lice and are discussed below in greater detail.
Guidelines
The AAP published guidelines on the diagnosis and management of head lice infestation in 2010. In this report, the OTC products permethrin 1% or pyrethrin are recommended as first-line therapy, unless resistance is known to occur in the community. Permethrin is labeled for use in those aged at least 2 months, and pyrethrin is labeled for use in those aged at least 2 years.
The most recently published recommendations come from the AAP’s 2012 Red Book, and these OTC products continue to be recommended as initial pharmacotherapy of head lice. Advantages of these OTC products include availability without prescription, inexpensive cost and good safety profiles. Their major disadvantage includes resistance by head lice. Resistance (in vitro and clinical) to permethrin and pyrethrin has been well documented in the literature. What is less well known, however, is the geographic prevalence of resistance. It can be difficult to accurately access resistance prevalence in a community, as information may be based solely upon anecdotal reports (ie, not standardized assessment techniques).
Common treatment errors
Before concluding that resistance is the cause of treatment failure when permethrin- or pyrethrin-based OTC products are used, it is wise to consider other potential factors. These factors include: 1) improper use of the OTC product (eg, improper application time); 2) re-infestation; or 3) misdiagnosis. It is important to stress proper product use, as it can be easy for caregivers to use these products incorrectly. For example, hair conditioners or conditioning shampoos should not be used just before use of the OTC products, as they can diminish their efficacy. It is often recommended to delay hair washing after treatment application for 2 or more days. Caregivers should be urged to follow product instructions very closely. Re-application of the product should be stressed to treat hatching lice and lice not killed with the first application.
Recommendations on when to apply the second treatment vary from 7 to 10 days. Another published recommendation includes a three-treatment strategy, with treatment on days 0, 7 and 13 to 15, to more closely mimic the louse life cycle.
Prescription products
Clinicians can now choose from four FDA-labeled prescription products when permethrin- or pyrethrin-based OTC products fail, or when lice display resistance. These prescription products differ by application time, FDA-labeled ages, precautions with use, ovicidal activity and cost. Third-party insurance and state Medicaid coverage will affect actual product cost to families. Direct comparative clinical trials of these products are not available. As most of these products are new to the commercial market, there are no published reports of clinical resistance.
Reports of head lice in Europe resistant to malathion have been published. The product formulation used in the United States, however, differs from that used in Europe, and the US product has not been available as long as in Europe, which likely contributes to the lower resistance patterns seen in the United States. In the clinical report published in 2010 by the AAP, benzyl alcohol 5% and malathion 0.5% are recommended for treatment failure or resistance to the OTC products. Spinosad and ivermectin lotion were not approved for use when this report was published. The 2012 Red Book does not differentiate among these four topical prescription products with respect to efficacy and recommends their use when treatment failure occurs with the OTC products.
Ivermectin has also been evaluated in published controlled clinical trials as oral therapy for head lice. It is not, however, FDA-labeled for this use. A large, randomized controlled trial that evaluated oral ivermectin in children aged 2 years and older was published in 2010. Two 400-mcg/kg doses of ivermectin were given on days 1 and 8 and then compared with malathion in children recruited from the United Kingdom, Europe and Israel. Children who failed malathion therapy in the previous 2 to 6 weeks were included in this study. The malathion product used in this study differs from the US product, and the US product contains additional formulation compounds that contribute to its pediculocidal activity. In the per-protocol population, 97.1% of children receiving ivermectin were free of live lice on day 15 (primary outcome measure), as compared with 89.8% of children receiving malathion (P<.05).
There were no differences in adverse effects between the two treatment groups. Ivermectin has also been evaluated in published studies using a 200-mcg/kg dose. Efficacy rates have been greater with the 400-mcg/kg dosing. Oral ivermectin should not be given to children weighing less than 15 kg, as adverse effects may be greater. The 2012 Red Book describes oral ivermectin’s role as consideration for use when treatment failure occurs with all topical agents.
There is no role for the use of additional agents that have been touted by some as alternative therapies, such as oral trimethoprim-sulfamethoxazole, permethrin 5%, or crotamiton. These products are not FDA-labeled for treatment of head lice infestation, and fewer data support their efficacy.
References:
Ameen M. Pediatr Infect Dis J. 2010;29:991-993.
Chosidow O. Engl J Med. 2010;362:896-905.
Cole SW. Ann Pharmacother. 2011;45:954-958.
Frankowski BL. Pediatrics. 2010;126:392-403.