Resistance is futile

With more than 12 million outbreaks estimated to occur annually among preschool and school-aged children in the United States, lice infestations are a big deal. And pharmacists play a key role in helping parents select safe and successful treatments.

According to a whitepaper published earlier this year by TyraTech, makers of Vamousse, lice resistance to permethrin and synergized pyrethrins has limited the efficacy of OTC products containing these pesticides and engendered their misuse and overuse.

“The optimal treatment for pediculosis should act rapidly and reliably to eliminate live lice and eggs, and be easy to use, safe and affordable,” wrote Cheryl Krader, author of the whitepaper. “Over-the-counter agents are recommended as first-line intervention for pediculosis, and products containing pesticides that act chemically as neurotoxins have been used most commonly in the United States. However, those traditional treatments have fallen short of meeting the optimal treatment criteria with the advent of “super lice,” or lice that have developed a resistance to those neurotoxins. “The pesticide-based products have been associated with increasing failure rates that are attributed to high levels of genetic-based louse resistance and low efficacy for eliminating eggs,” she said.

In recent North American studies, strains of lice carrying genes for resistance to popular pediculicides ranged from 97.1% and 99.6% of lice. That has contributed to highly variable effectiveness rates of pesticide treatments between 45% and 80%.

Resistance and lower efficacy are compounded by the fact that subsequent pediculicide treatments cannot be reapplied until at least seven to as many as 10 days have passed. This increases the likelihood of spreading the lice infestation if the first treatment proves ineffective.

“The inconsistent efficacy and safety concerns associated with pesticide-based treatments for pediculosis are driving a need for alternative treatments,” Krader concluded. “Products with a physical mode of action offer a high-safety profile and are less susceptible to the development of resistance,” she added. “From 2014 to 2016, unit sales in the United States of such pesticide-free, physical mode of action products for treating pediculosis rose from 31% to 41% of total branded product sales.”

To download the full Super Bugs report, click here.