Researchers published in the New England Journal of Medicine new safety and efficacy data for ivermectin lotion, the newest weapon in the millennia-old battle against head lice.
In two multisite, randomized, double-blinded studies, Dr. David M. Pariser of Eastern Virginia Medical School, Norfolk, and his associates found that a single 10-minute application of 0.5% ivermectin lotion eliminated live lice in nearly 95% of patients at day 2 without the need for nit combing, with around 74% remaining lice-free 15 days after the application (N. Engl. J. Med. 2012;367:1687-93).
Dr. David L. Hill
The studies evaluated a total of 765 patients aged 6 months and older. The vast majority of subjects were children, reflecting the typical distribution of head lice in the population. Control patients received an identical 10-minute application of the inert vehicle. The most common adverse events in both groups were itching, scratching, and redness of the skin, occurring at rates of over 1% in the control group and less than 1% in the treatment group.
Earlier this year, topical ivermectin (Sklice, Sanofi-Pasteur) joined the growing list of medications approved by the Food and Drug Administration for use against lice. Increasing reports of lice resistant to the traditional first-line therapies of permethrin and pyrethrins have driven interest in alternative therapies. Lindane shampoo, an older alternative treatment, is no longer recommended because of safety concerns.
While solid numbers are lacking, the Centers for Disease Control and Prevention estimates that 6-12 million Americans suffer louse infestations annually, with children between the ages of 3 and 11 years accounting for the bulk of cases. The annual economic impact of infestations runs around $1 billion. In addition to itching and scratching, lice can cause skin infections such as impetigo and, rarely, infection by Bartonella quintana (trench fever). Additionally, those infested suffer from the stigma of being thought unclean, even though in reality lice infestations are not associated with hair length, hygiene practices, or social class.
More than 45 million people worldwide have taken the oral form of ivermectin to treat nematode infections, and some doctors have prescribed it off label to treat lice and scabies when conventional treatments have failed. Permethrin and pyrethrins paralyze lice by modifying voltage-gated sodium channels, so that resistance to one agent usually confers resistance to all of them.
Ivermectin, on the other hand, acts primarily at glutamate-gated chloride ion channels, making it a useful second-line therapy. Researchers also point out that while malathion is the only currently approved therapy that kills louse eggs, ivermectin does seem to penetrate the eggs and kill nymphs shortly after they hatch.
Despite this study, I’m likely to continue to keep ivermectin as a backup therapy and not start using it as frontline treatment. The American Academy of Pediatrics Red Book still recommends using 1% permethrin or pyrethrins (both available over the counter) first line. If, 24 hours after appropriate use, live lice are still visible in the hair, then other second-line options include benzyl alcohol lotion, malathion, or spinosad suspension. Compliance rates with malathion appear to be around 50%, presumably because it’s the only one of the treatments that has to remain in the hair for 8-10 hours. Head-to-head comparisons (so to speak) of these interventions remain to be performed. Folk remedies such as petroleum jelly, olive oil, butter, or mayonnaise have never been proven to be effective therapies.
I always try to remind parents of children with lice that lice cannot jump, and they can only survive a few hours away from the human scalp. Hats, combs, clothing, and sheets rarely serve as fomites for louse transmission, and washing these items in hot water should easily kill any remaining lice and nits. Since louse egg sacs (nits) may cling tenaciously to hair shafts long after all the lice are killed, children with nits may return to school so long as they no longer have any living lice visible in the hair.
The studies were funded by Topaz Pharmaceuticals (now Sanofi-Pasteur). Ms. Bell reported receiving consulting fees from Topaz Pharmaceuticals and Sanofi Pasteur. Dr. Ryan reported being a former employee of Topaz Pharmaceuticals, receiving consulting fees and stock or stock options from Topaz Pharmaceuticals, and receiving consulting fees and payment for manuscript preparation from Sanofi Pasteur. Ms. Meinking reported receiving a grant on consulting fees from Topaz Pharmaceuticals. Dr. Pariser said he had no other relevant potential conflicts of interest.
Dr. Hill is vice president of Cape Fear Pediatrics in Wilmington, N.C., and is an adjunct assistant professor of pediatrics at the University of North Carolina at Chapel Hill. He is a member of the editorial advisory board of Pediatric News, and the author of Needles, a weekly blog, at www.pediatricnews.com.