Trying to Keep Ahead of Lice: A Therapeutic Challenge

C. E. Malcolm, MD, CCFP; J. N. Bergman MD, FRCPC


Skin Therapy Letter. 2006;11(10):1-6. 

In This Article


The ideal treatment agent for lice would be free of harmful chemicals, readily available without a prescription, easy to use, and inexpensive.[5] Chemical pediculicides are currently the standard treatment.

Prior to the emergence of resistance, the treatment of choice in North America was permethrin 1% due to its safety and efficacy. Unfortunately resistance to permethrin and lindane is common in populations where these pediculicides have been heavily used.[3] To illustrate this, the insecticidal activity of pyrethroids in the mid 1980s was 100%, but by 2000 it had decreased to only 28%.[6] Conversely Meinking, et al., in a recent study, showed 1% lindane was the slowest and least effective pediculicide with no lice eradicated after 10 minutes (the recommended application time), and killing only 17% of lice after 3 hours.[7] Malathion (Ovide®, Taro Pharmaceuticals), which had not been used extensively in the US, has performed well in permethrin-resistant populations.[3] Lice resistance to both pyrethrin and malathion has been documented in the UK (Downs, et al. showed a 64% failure rate for malathion).[8] The pattern of resistance in an area generally follows the pattern of pediculicide use, and this geographic variation in sensitivities further reinforces the belief that lice adapt to toxins and develop resistance with ongoing exposure.


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