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Letters

Clinical efficacy of treatment for head lice

BMJ 1995; 311 doi: https://doi.org/10.1136/bmj.311.7016.1369 (Published 18 November 1995) Cite this as: BMJ 1995;311:1369
  1. Manice Stallbaumer,
  2. Joanna Ibarra
  1. Community hygiene concern resource project leader Hospital for Tropical Diseases, London NW1 0PE
  2. Community hygiene concern programme coordinator London N8 9JT

    Counting head lice by visual inspection flaws trials' results

    EDITOR,--In their review of drug treatments for head lice Robert H Vander Stichele and colleagues identified only seven clinical trials in the past 29 years that met their evaluation criteria.1 However, visual inspection (their main measure for clinical evaluation) is flawed.2 Furthermore, to determine ovicidity a comparison of the hatching rate of treated and untreated eggs after incubation, to simulate the conditions on the head, is necessary.3

    Use of a hand lens to detect hatchlings on the head is impractical because lice move rapidly away from disturbance in dry hair. Mathias et al found the application of isopropanol alcohol to be helpful as it causes lice to fall from the head.4 Other workers use a fine toothed comb to detect lice. Nevertheless, none of these methods is sufficiently controlled to replace incubation in the assessment of ovicidity.

    Vander Stichele et al barely touch on the question of resistance to insecticides. The evolution of genetically selected tolerance when an insect population is repeatedly exposed to a compound on a piecemeal basis is inevitable. Thus, although a product may work satisfactorily when it is submitted to a clinical trial, the situation changes after years of use. Cross resistance between compounds in the same chemical group is well documented, and multiple resistance may also occur.5 Moreover, the results of trials conducted on a louse population in one country are not valid in another country or region, where the history of exposure to pesticides of the lice is different. Consideration of these factors does much to throw light on the high prevalence of head lice noted by Vander Stichele and colleagues “although treatments abound.”

    References

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