1. Home>
2. Specialties>
3. Dermatology>
4. Summary and Comment

Scratching Your Head Over Resistant Head Lice

Physicians treating resistant head lice in the U.S. still have a good alternative.

Infestation with head lice is common in children throughout the world. In parts of the U.S. and elsewhere, these parasites are becoming increasingly resistant to the most frequently used therapeutic agents. In this in vitro, partially manufacturer-supported study, researchers compared the effectiveness of 1.0% permethrin and 0.5% malathion, alone and in their respective commercial preparations, Nix and Ovide, by exposing head lice to filter paper impregnated with the drugs. The lice were obtained from three U.S. locations and from a location in Ecuador where resistance was deemed unlikely. DNA sequencing was used to test for the presence of two mutations known to confer permethrin resistance.

Malathion rapidly killed all lice, whether sensitive or resistant to permethrin, and its effects were a bit more rapid than the effects of permethrin in the lice that were susceptible to that agent. In the permethrin-resistant lice, which were collected in southern Florida, Ovide produced slightly faster effects than malathion alone, suggesting that other ingredients in that preparation have pediculicidal activity. Almost all of the resistant lice had evidence of the mutations.

Comment: Failure to eradicate Pediculus capitis may be the result of improper use of the treatment product, reinfestation, or lack of susceptibility to the preparation used. The frequency of permethrin resistance is unknown, but in patients who fail to respond to this agent, an effective alternative is Ovide. In the U.S. where malathion has had little use, lice should be susceptible to it. Malathion-resistant lice have been reported in the U.K., where the drug has been more widely prescribed. Thus, combination therapy may someday be necessary to thwart the emergence of resistance.

— Jan V. Hirschmann, MD

Published in Journal Watch Dermatology September 23, 2003

Citation(s):

Yoon KS et al. Permethrin-resistant human head lice, Pediculus capitis, and their treatment. Arch Dermatol 2003 Aug; 139:994-1000.

• Original article (Subscription may be required)
• Medline abstract (Free)

Elston DM. Drug-resistant lice. Arch Dermatol 2003 Aug; 139:1061-4.

• Original article (Subscription may be required)
• Medline abstract (Free)