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Treatment of head lice: Update on effective therapies
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Head lice infestation is a common problem among children and can pose significant challenges for treatment.
Fortunately, three new products have been labeled by the FDA for use in infants and children as young as 6 months of age during the past 4 years. These new products are needed, as resistance to the commonly used products that are available over-the-counter, permethrin- and pyrethrin-based products (eg, Nix [Insight Pharmaceuticals] and Rid [Bayer HealthCare]), is increasing.
Edward A. Bell
Complicating this concern of resistance, however, is a lack of standardization of how resistance is determined and defined. When a parent tells a health care provider, “Nix and Rid (or their generic equivalents) didn’t work — my child still has lice,” the health care provider may wonder if it is truly resistance. Or did the parent possibly use the product properly, including applying a second treatment 7 days after the first. The child could possibly have been re-exposed and infested again. These issues can affect what treatments are next used.
Resistance by head lice to permethrin- and pyrethrin-based products certainly is possible, as it has been evaluated and documented in numerous published clinical studies. The pharmacologic mechanisms of action for permethrin and pyrethrin include inhibition of sodium ion influx, causing louse paralysis. Amino acid substitutions in this sodium ion channel result in resistance to the effects of these insecticides, and the gene encoding for these substitutions has been called the knockdown resistance (kdr)-like gene.
Kdr-like gene a potential factor
Complicating this are data demonstrating children infested with lice that possess the kdr-like gene can still be successfully treated with permethrin or pyrethrin. Resistance by head lice to permethrin or pyrethrin as determined by laboratory or bioassay testing does not always correlate with clinical treatment failure, and this has been demonstrated in the published literature. Thus, other factors must be at play, such as insecticide exposure time. Additional data are needed to better define resistance of head lice to these commonly used products, and its clinical implications.
Given that resistance to permethrin and pyrethrin can vary geographically, and that resistance is not well defined or standardized, it is still reasonable to initiate treatment in an infested child with a permethrin- or pyrethrin-based product. These are the recommendations described in the latest AAP Red Book and in the latest AAP clinical guideline (2010). When OTC head lice products are used, it is important to emphasize to caregivers the importance of following product instructions very carefully. This includes application of a second treatment 7 days after the first treatment. Some experts have advocated a three-treatment strategy, with treatment on days 0, 7 and 13 to 15, which more closely mimics the louse life cycle. Additional useful recommendations include not using hair conditioners or conditioning shampoos just prior to product application, and to delay hair washing for 2 or more days after product application.
Effective topical products
If these products fail to eradicate head lice, and re-infestation has been ruled out, health care providers now can choose from four FDA-labeled topical products: malathion (Ovide, Taro Pharmaceuticals), benzyl alcohol (Ulesfia, Shionogi), spinosad (Natroba, ParaPRO/Pernix Therapeutics), and ivermectin (Sklice, Sanofi-Pasteur). All are likely to be effective. Ulesfia and Sklice can be used on infants as young as 6 months, and Ovide can be used on infants aged at least 24 months. Clinical resistance to these products is not currently a concern. Which product to use for a specific patient may be dictated by insurance or state Medicaid preferences.
Natroba and Sklice can be expensive to use, especially for children with long hair, as multiple bottles may be necessary. To help offset these costs, coupons are available for Sklice, Ovide and Ulesfia. Ovide and Sklice may have better ovicidal activity, although a second treatment may still be necessary in 7 days. Prescribers also can consider using orally administered ivermectin (400 mcg/kg and repeated in 7 days), as a published controlled trial has demonstrated its effectiveness. Ivermectin is not FDA-labeled for this use, however, and it should not be given to younger children (those weighing less than 15 kg).
Other products available OTC or by prescription (eg, trimethoprim-sulfamethoxazole or permethrin 5%) are not likely to be effective and should not be used.
This image is an enlarged view of a female head louse.
Image: CDC/Reed & Carnrick Pharmaceuticals
Thus, where are we with the treatment of head lice? There is bad news and good news. The bad news relates to increasing resistance to commonly used OTC products. The good news is there are now four topical products and one oral product that should be effective. That’s good news for our patients, and bad news for head lice.
References:
R. New Engl J Med. 2011;364:386-387.For more information:
Edward A. Bell, PharmD, BCPS, is a professor of clinical sciences at Drake University College of Pharmacy, Blank Children’s Hospital, in Des Moines, Iowa. He is also a member of the Infectious Diseases in Children Editorial Board. He can be reached at: Drake University College of Pharmacy, 2507 University Ave, Des Moines, IA 50311; email: ed.bell@drake.edu.Disclosure: Bell reports no relevant financial disclosures.