What is the role of pyrethrin and permethrin in the treatment of pediculosis and pthiriasis (lice infestation)?

Updated: Aug 16, 2019
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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Pyrethrin and permethrin kill live lice, but not unhatched eggs. A second treatment 9-10 days after the first treatment is recommended in order to kill any newly hatched lice before they can produce new eggs. Pyrethrin is derived from chrysanthemums and is approved for use in children aged 2 years or older. It should not be used by individuals who are allergic to chrysanthemums or ragweed. Piperonyl butoxide has been added to pyrethrin products to enhance efficacy and to minimize the potential for resistance. [6]

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