Controlled study of malathion and d-phenothrin lotions for Pediculus humanus var capitis-infested schoolchildren

Abstract

SummaryAnecdotal reports have suggested that reduced efficacy of pediculicides against Pediculus humanus capitis could be related to resistance to treatments.Ovicidal and pediculicidal activities of 0.5% malathion and 0.3% d-phenothrin lotions 'were tested in an experimental model of P humanus capitis grown on rabbits to ensure that the two treatments were pharmacologically equipotent. We then did a randomised controlled trial in which the lotions were administered to 193 P humanus capitisinfested schoolchildren (malathion, 95; d-phenothrin, 98). Success rate was defined as the absence of both live lice and viable nits. Before treatment, live lice were collected and subjected to a pediculicidal test. Pharmacological tests showed 100% killing of the rabbit-grown nits and lice after exposure to both pediculicides. On day 1 of the controlled trial, the success rate was 92% in the malathion group (95% CI, 0-86-0.97) and 40% in the d-phenothrin group (0.30-0.49) (pc0.0001); on day 7, it was 95% in the malathion group These results suggest an acquired resistance to d-phenothrin in the schoolchildren tested, since all other conditions of the administration of insecticides were standardised.

COMPARATIVE EFFICACY OF d-PHENOTHRIN AND MALATHION IN THE CONTROL OF PEDICULOSIS

“…not compare well with the findings of other workers [5]. The pediculicidal activity of malathion and d-phenothrin as observed in this study is 82 and 84 per cent respectively whereas Chosidow et al report 95 per cent and 39 per cent pediculicidal activity for malathion and d-phenothrin respectively [5]. This difference is due to the acquired resistance to d-phenothrin in France as reported in the above quoted study.…”

Three mutations identified in the voltage-sensitive sodium channel α-subunit gene of permethrin-resistant human head lice reduce the permethrin sensitivity of house fly Vssc1 sodium channels expressed in Xenopus oocytes

“…Over the last two decades, resistance to pyrethrins and pyrethroid insecticides by the human head louse, Pediculus humanus capitis, has been widely documented (Burgess et al, 1995;Downs et al, 1999a;Downs et al, 1999b;Chosidow et al, 1994;Mumcuoglu et al, 1995;Hemingway et al, 1999;Rupes et al, 1995;Picollo et al, 1998;Vassena et al, 2003;Yoon et al, 2003;Yoon et al, 2004;Lee et al, 2000b). Heightened public and governmental concerns have occurred because of increased incidents of head louse infestations among school children (http://www.cdc.gov/ncidod/dpd/parasites/lice/default.htm; http://www.headlice.org).…”

L’essai clinique randomisé par grappes

“…La seule unité de randomisation logique est donc l'hôpital. Une autre motivation à randomiser des grappes est la crainte d'une contamination entre les groupes (voir [5] qui compare deux lotions antipédiculaires), ou dans les études prophylactiques (situations dans lesquelles la randomisation par grappes permet d'éviter qu'un sujet ne perde sa susceptibilité à être infecté, tout simplement parce qu'il évolue au milieu de sujets immunisés par le traitement étudié). C'est également le cas lorsque l'on souhaite étudier un programme de prévention : des interactions actives entre les sujets des deux bras de randomisation (le bras expérimental et le bras témoin) pourraient en effet largement contaminer le bras témoin.…”