Baltimore—With school back in session, parents frantically pulling boxes of head lice treatments off the drugstore shelves might not welcome this news: A recent review on head lice treatments available in the United States described a notable decline in the effectiveness of permethrin/synergized pyrethrins.

A report published in the journal Pediatric Dermatology suggests the resistance likely was caused by widespread and indiscriminate use of pyrethroids over 30 years, especially with its widespread use in schoolchildren with lice.

Study authors, led by researchers from the Division of Pediatric Dermatology at Johns Hopkins Medicine, also point out that the potential toxicity of lindane, and the availability of safer and more effective alternatives, should limit its use.

The report notes that prescription products found to be safe and effective include malathion, benzyl alcohol, spinosad, and topical ivermectin, but that home remedies such as petroleum jelly, mayonnaise, and essential oils have not been demonstrated as safe or effective and could cause adverse reactions.

“Our findings indicate that over-the-counter treatments for head louse infestations are no longer likely to be effective,” pointed out co-author Terri Meinking, PhD, of the Global Health Association in Miami.

“The lesson we should learn is that those products that do remain effective, which are available by prescription, should be used judiciously so that they do not suffer the fate that has befallen the pyrethroids,” added lead author Ellen Koch, MD.

Background information in the article notes that filling of prescriptions for the treatment of infestations had a seasonal peak in July to September for 2012 to 2014, coinciding with the back-to-school period. The study also notes that prescriptions have increased about 4% each year, possibly because of more infestations or more infestations failing nonprescription OTC or home remedy approaches.

While widespread use of pyrethroids has precipitated their current ineffectiveness in the treatment of infestations, according to the report, two recently approved products—spinosad and topical ivermectin—have been found to be effective without nit combing.

“The availability of proven and safe prescription remedies offers the opportunity to manage head louse infestations strategically and effectively. Given the current situation of resistance and apparent inefficacy of OTC treatments,” study authors write, healthcare providers “should understand how to manage head lice infestations, take an active role in the diagnosis of infections, and guide appropriate use of well-tested, proven, FDA-reviewed products.”

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