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Head lice in children have been treated for years with lotions, creams and shampoos. But lice are getting wise, becoming resistant to all of them. Now in a study in the New England Journal of Medicine, researchers report that a tablet taken by mouth may be an alternative when standard treatments fail.

NPR's Patti Neighmond reports.

PATTI NEIGHMOND: To say lice have been around a long time is something of an understatement, according to pediatrician Barb Frankowski.

Dr. BARB FRANKOWSKI (Pediatrician): They found head lice in mummies, Egyptian mummies.

NEIGHMOND: Thousands of years ago, and they're still here, in large part, Frankowski says, because like most bugs they evolve faster than the substances developed to kill them. And lice are definitely bugs, she says. An adult louse is about the size of a sesame seed.

Dr. FRANKOWSKI: If you look at it under the microscope, it looks like a little insect. You can see its mouth and its little legs and you can actually tell, if you're that good at it, under a microscope whether it's a male or a female.

NEIGHMOND: And the eggs that hatch, called nits, are extremely sturdy, sticking to the hair shaft sort of like glue. Like a mosquito, lice survive by sucking blood - only human blood, by the way. They don't like cats, dogs or inanimate objects. For years shampoos, cream rinses and lotions that contain insecticides have killed off the lice. But that's changing, says Frankowski, who helped develop guidelines for pediatricians who treat lice.

Lice have become resistance to treatment, she says, and that's why researchers from Europe looked at a powerful oral medication, which is now used to treat certain parasites in people, as well as worms in horses and dogs. Dermatologist Olivier Chosidow headed a study with patients whose lice weren't eradicated by topical treatments. He compared the drug ivermectin, which attacks the central nervous system of lice to the prescription lotion, malathion.

Dr. OLIVIER CHOSIDOW (Dermatologist): The lice are blood suckers.

NEIGHMOND: So, they absorb the ivermectin when they're feeding on blood. The drug is toxic to their central nervous system. Ivermectin is used once to kill off the lice and then about a week later to kill off any eggs. Chosidow, who has worked for various drug companies as a consultant, found ivermectin 10 percent more effective than the lotion. It was 95 percent successful in killing the hard-to-treat lice. The findings are promising, says pediatrician Cindy Devore, who works with schools helping them treat children with lice.

Dr. CINDY DEVORE (Pediatrician): But what we don't want to do is to jump in immediately using a very good, potentially stronger or more effective treatment, when a lesser drug might do the same job. We don't want to bring out the big guns because we do not want head lice to develop resistance to ivermectin.

NEIGHMOND: Ivermectin has not been approved by the FDA to treat head lice. European researchers agree with Dr. Devore that if the drug is used in the U.S., it should be used only after shampoos, cream rinses and prescription lotions have failed. And, even though the study found no serious side effects, some health experts worry that because Ivermectin works by destroying the nervous system of lice, it could be potentially harmful to people.

Patti Neighmond, NPR News.

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