Products commonly used to treat head lice may not always be effective in children who become reinfested. Permethrin is the main ingredient in several commonly used head lice products. The investigators found that a certain proportion of the small sample of lice tested (from American children) was resistant to permethrin, and increasing the dosage did not increase the effectiveness. In contrast, approximately half of the head lice taken from children in Borneo were killed at lower concentrations of permethrin, and virtually all of them were killed at higher doses.
Virtually all of the American children involved in the study had been previously treated with an insecticide for head lice. The most common preparation used was Nix, and the second most common was RID, A-200. That head lice taken from these children seemed resistant to the insecticide could indicate a problem with parents not following product directions as closely as they should.
The group's findings confirm media reports that some head lice are becoming resistant to permethrin-containing products used in the US. Parents need to understand that the 'cement' with which the female louse attaches the egg to the hair shaft is hard to dissolve with any product, and that long after head lice have been killed, hatched and dead eggs may remain in the hair. Researchers advise parents to remove any dead or hatched eggs from the hair with a fine-toothed comb. Head lice are not as infectious as people think they are. Although head lice are a nuisance and have a negative image, this is not meningitis, he stressed. Children should not be excluded from school even if they have an active infestation and certainly not if they only have eggs because head lice do not cause disease.
Archives of Pediatrics and Adolescent Medicine September, 1999;153:969-973.
COMMENT: It seems that several decades of using Nix has caused it to become virtually worthless for the treatment of head lice. I would strongly advise not using it and merely restricting the treatment to aggressive combing with a nit comb, which a previous study cited in this newsletter earlier this year seemed to support as an effective alternative. Certainly it is safer and less expensive. It does not seem to make any sense to expose children to these toxic chemicals when there is a greater than 50% chance that the lice will be resistant anyway.