In a systematic review of randomized trials, a total of 28 trials were evaluated 1. Of the 14 trials with low to moderate risk of bias, 7 were selected for review because they used the same outcome measure (absence of live lice or viable nits on day 14). Only permethrin 1% cream rinse showed efficacy in more than two studies, with the lower 95% confidence limit of cure rate above 90%. Lindane and the natural pyrethrines are not sufficiently effective to justify their use.
Of 70 identified studies, only four met the inclusion criteria of a Cochrane review 2 (abstract , review [Abstract], withdrawn from the Cochrane Library) and one is awaiting assessment. There was no evidence that any of the pediculicides has greater effect than another. The two studies comparing malathion and permethrin with their respective vehicles showed a higher cure rate for the active ingredient. Another third study comparing synergised pyrethrins with permethrin showed their effects to be equivalent. A comparative trial of malathion lotion vs combing, showed combing to be ineffective for the curative treatment of head lice. Adverse effects reported in the trials were all minor.
Comment: According to Burgess, resistance to permethrin and to malathion is widespread in the UK.
Another systematic review 3 including 7 RCTs with a total of 1,808 subjects was abstracted in DARE. Most studies had a cure rate at 14 days of higher than 80%. A number of studies reported the lower 95% CI of cure rates as higher than 90% for permethrin. Only one study reported this for carbaryl or malathion. The combined odds ratio of treatment failure for lindane versus permethrin was 15.1 (95% CI 7.99 to 28.84) for the largest two trials.
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