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Efficacy and safety of a dimethicone lotion in patients with pyrethroid-resistant head lice in an epidemic area, Okinawa, Japan.

ABSTRACT: Pyrethroid insecticides are the only pesticides approved for the treatment of head lice (pediculosis capitis) infestations in Japan. However, in Okinawa Prefecture, 96% of head lice are resistant to pyrethroids. Here, we conducted a clinical trial to assess the safety and efficacy of a dimethicone preparation against head lice infestations in Okinawa Prefecture. Dimethicone-containing lotion was applied over the entire scalp three times over a 7-day period. Lice bodies (nymphs/adults) and eggs (nits) were counted before (day 0) and after treatment (day 8); a subset of eggs was collected to estimate viability based on hatch rate. Efficacy was evaluated based on improvement (reduction) in head lice counts post-treatment with respect to baseline. Safety was evaluated based on subjects' scalp condition and adverse event incidence. Utility was a composite end-point combining efficacy and safety. In total, 35 subjects were enrolled. Efficacy and safety were evaluated in 23 and 35 subjects, respectively. No side-effects of note were reported during the treatment period. The dimethicone lotion resulted in a utility rating of "marginally useful" or higher in over 80% of the study population, signifying the formulation to be both safe and effective. The dimethicone lotion was also a potent ovicide; 99.4% of eggs collected after treatment failed to hatch when incubated. Eradication of head lice remained successful for at least 4 weeks after the final topical dimethicone application in 25 of the 28 subjects reached by telephone survey. Lice bodies and eggs were genotyped to analyze the prevalence of three knockdown resistance (kdr)-type mutations within the voltage-sensitive sodium channel known to confer pyrethroid resistance. One or more kdr mutations were confirmed in 30 of the 32 subjects from whom specimens were collected (93.8%). Dimethicone was confirmed to be both safe and effective in treating pyrethroid-resistant head lice.

SUBMITTER: Yamaguchi S

PROVIDER: S-EPMC8453846 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Context. During the late 1990s, insecticide resistance had rendered a number of treatment products ineffective; some companies saw this as an opportunity to develop alternative types of treatment. We investigated the possibility that a surfactant-based lotion containing 10% cocamide diethanolamine (cocamide DEA) was effective to eliminate head louse infestation. Settings and Design. Initial in vitro testing of the lotion formulation versus laboratory reared body/clothing lice, followed by two randomised, controlled, community-based, assessor blinded, clinical studies. Materials and Methods. Preliminary laboratory tests were performed by exposing lice or louse eggs to the product using a method that mimicked the intended use. Clinical Study 1: Children and adults with confirmed head louse infestation were treated by investigators using a single application of aqueous 10% cocamide DEA lotion applied for 60 min followed by shampooing or a single 1% permethrin creme rinse treatment applied to pre-washed hair for 10 min. Clinical Study 2: Compared two treatment regimens using 10% cocamide DEA lotion that was concentrated by hair drying. A single application left on for 8 h/overnight was compared with two applications 7 days apart of 2 h duration, followed by a shampoo wash. Results. The initial laboratory tests showed a pediculicidal effect for a 60 min application but limited ovicidal effect. A longer application time of 8 h or overnight was found capable of killing all eggs but this differed between batches of test material. Clinical Study 1: Both treatments performed badly with only 3/23 (13%) successful treatments using cocamide DEA and 5/25 (23.8%) using permethrin. Clinical Study 2: The single overnight application of cocamide DEA concentrated by hair drying gave 10/56 (17.9%) successes compared with 19/56 (33.9%) for the 2 h application regimen repeated after 1 week. Intention to treat analysis showed no significant difference (p = 0.0523) between the treatments. Over the two studies, there were 18 adverse events possibly or probably associated with treatment, most of which were increased pruritus after treatment. Conclusions. Cocamide DEA 10% lotion, even when concentrated by hair drying, showed limited activity to eliminate head louse infestation.

Project description:IntroductionSilicones (e.g., dimethicone) are effective and safe alternatives to insecticides for the treatment of head lice. However, silicones are lipophilic substances and do not only leave the hair greasy but they are also difficult to wash out. We have evaluated the efficacy and safety of a potential solution to this problem: an aqueous dispersion of a novel silylated polyol that has the same mode of action as dimethicone (suffocation) without its negative impact on hair characteristics.MethodsThis was a randomized, controlled, investigator-blinded, bicentric study that was conducted at two locations in the state of Florida (USA) to compare the test product (medical device) to a pyrethrum-based pediculicide that is a first-line, prescription-free treatment against head lice in the USA. The subjects (n = 70) were randomly divided into two groups of 35 persons (test product group and reference product group), with each participant receiving two applications (day 0 and 7) of the product to be tested, according to the instructions for use. Efficacy and safety was evaluated at distinct time points. The primary objective was to establish a cure rate for the test product that was better than 70% at study end (day 10). Esthetic effects of the test product versus dimethicone were evaluated in a blinded, cross-over consumer study (n = 100).ResultsAt study end, the cure rate (corrected for re-infestation) of 88.2% with the test product significantly surpassed the pre-defined target of 70%, and thus the superiority of the test product versus the reference product was confirmed. The number of subjects cured (free of head lice) after the first treatment was remarkably higher with the test product than with the reference product (57.1 vs. 2.9%, respectively). Both products were safe and well tolerated and both showed beneficial esthetical effects. The consumer test demonstrated that the test product had better washing-out properties than dimethicone, as reflected by a significantly lower average rinsing time and number of washings required to restore the visual aspect of the hair, especially in terms of greasiness.ConclusionAqueous dispersions of silylated polyols are a promising new class of pediculicides that combine high cure rates with optimal user convenience (short treatment period, easy wash-out with positive effect on hair quality).Trial registrationClinicalTrials.gov identifier, NCT03617926.FundingOystershell Laboratories.

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Efficacy and safety of a dimethicone lotion in patients with pyrethroid-resistant head lice in an epidemic area, Okinawa, Japan.

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