Head Lice Growing Resistant to Standard Meds
It's probably time to turn to newer treatments, study suggests
DNA sampling revealed that more than 88 percent of the lice found in both countries carried the specific TI mutation that is associated with the kind of nerve insensitivity that makes lice resistant to standard over-the-counter permethrin medications.
In the United States alone, the researchers pegged TI frequency in an average of roughly 84 percent of the lice population between 1999 and 2009. But a closer look at the final years of this timeframe revealed that the rate actually began to approach 100 percent of the lice population between 2007 and 2009.
Accordingly, Clark and his associates concluded that the need for new treatments for lice has reached a critical stage.
"Europe and South America actually stopped using these pyrethroid compounds years ago," he said. "It's not that these compounds aren't in themselves good formulations. But the very last thing you want to do is treat a single pest population with one compound that has one mode of action for years and years -- and that's exactly what we did. The result is that these compounds are just not effective anymore."
"But the good news is that over the last three years we have seen four or five new compounds entering the market," said Clark, in reference to drugs that include the brands Ulesfia, Sklice and Natroba.
"They all have different kinds of compounds and mechanisms, and they're all already commercially available," he said. "This will lead to what's called redundant killing, where if one compound doesn't do the job, the other compound will. So there is a way forward."
Dr. David Pariser, a professor of dermatology at Eastern Virginia Medical School, in Norfolk, agreed about the need to update treatment for head lice.
"I completely agree with this study's assessment regarding resistance, and with the thinking about the new drugs that we now have available," said Pariser, a former president of the American Academy of Dermatology. "I've had personal experience with one of them, as I was involved in the clinical trials, so I know they're very effective."
"More than that, they can actually be easier to use, as the older drugs would have to be applied repeatedly, whereas the new drugs are typically a one-time treatment," he said.
"However, I would add one nuance," Pariser continued. "While these new agents are great, they are prescription drugs, which means they are more costly. It may not be the actual insured consumer who will feel it if he's only paying a co-pay for the new meds, but certainly it's going to be a much bigger cost to the health care system as a whole."