The guts of human lice contain a specialized organ that harbors an unusual type of bacteria. These bacteria may aid the louse in digesting the blood meal or by providing essential nutrients. Certain antibiotics may affect or eliminate these bacteria from the louse’s gut, and body lice that have fed upon antibiotic-laden blood of people may be burdened and die. The effect of antibiotics on the health of head lice has yet to be determined conclusively. Physicians increasingly seem to prescribe combinations of the antibiotic agents trimethoprim and sulfamethoxazole (e.g. ‘Bactrim’, ‘Septra’) in attempts to treat head lice. We oppose this practice because these antibiotics are not approved as pediculicides, and they are valuable in fighting life-threatening infections. Their use for treating such a relatively innocuous condition as a louse infestation may accelerate the emergence or spread of bacterial resistance, thereby diminishing the usefulness of these antibiotics.
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