Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Topical Ivermectin Lotion for Treating Head Lice

In a situation of poor hygiene and shared living quarters, particularly overseas, you may acquire head and/or body lice, which make their homes predominantly in hair-covered areas of the body. The overwhelming symptom is itching. To search for head lice, inspect the scalp carefully. On close inspection, you may discover nits (white, ovoid 0.5 to 1 mm empty egg cases) attached to the hair shaft, or tiny 3-to-4 mm adult crawling forms in the scalp or (rarely) on the eyelashes. The nits remain attached to the hair, and move out with hair growth at a rate of approximately 0.4 in (1 cm) per month. A common finding is swollen lymph glands behind the ears or running down the back of the neck.

Fortunately, lice cannot leap or fly. It is often difficult to identify lice and mites by simple visual inspection of the scalp. A fine “nit comb” run through the scalp is better for detection. Wetting the hair may help. The treatment is to lather the body and scalp vigorously with crotamiton 10% (Eurax) lotion, leave the lather in place for 10 minutes, and then rinse.

For head lice, children may be treated with 5% permethrin (Elimite) cream in a single application; this is safe for infants over 2 months of age. Rub the cream into the skin and scalp, and wash it off after 8 to 12 hours. Comb the hair thoroughly in a direction toward the scalp to remove all nits. To be most effective, the process should be repeated in one week.

One percent permethrin cream rinse (Nix) or 0.5% malathion lotion (Ovide; approved for age 2 years and older) is also effective for removing lice from the hair. Apply it after the hair has been washed and towel-dried, leave it on for 10 to 20 minutes, and then rinse it off. Use a fine-toothed comb to remove the nits after rinsing. Comb again in one to two days. Repeat the treatment in 7 days to eliminate emerging lice. A treatment for resistant head and body lice is 0.3% pyrethium and 3% piperonyl butoxide (R and C shampoo, or RID) applied to all affected areas and washed off after 10 minutes.

In an article entitled “Topical 0.5% Ivermectin Lotion for Treatment of Head Lice” (New England Journal of Medicine 2012;367:1687-94), Dr. David Pariser and colleagues compared a single application of 0.5% ivermectin lotion with a control (inactive) substance for elimination of louse infestations without combing out the nits in persons 6 months of age and older. The topical ivermectin was applied to dry hair, left in place for 10 minutes, then rinsed with water. They found that the ivermectin was more effective than the control in eliminating head-louse infestations at one, 7, and 14 days after treatment.

In an accompanying editorial in the same issue of the journal, Olivier Chosidow and Bruno Giraudeau offered a perspective on this research. They noted that while oral ivermectin at a dose of 200 micrograms per kilogram of body weight has been taken by more than 45 million persons with a reasonable safety profile, topical ivermectin is not yet definitively proven safe, and its use may encourage emergence of ivermectin-resistant lice. They concluded that until further research is accomplished, we should continue to support the American Academy of Pediatrics recommendation to use 1% permethrin or pyrethrin insecticide as first-line therapy. If resistance in the community is known to be present or there are live lice present one day after treatment, then a switch to malathion may be useful. Until further notice, ivermectin should be the last choice.

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Tags: General Interest

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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.