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The mode of action of dimeticone 4% lotion against head lice, Pediculus capitis.

Abstract

BACKGROUND

Treatment of head lice using physically acting preparations based on silicones is currently replacing insecticide use due to widespread resistance to neurotoxic agents. It has been postulated that some products act by asphyxiation, although the limited experimental evidence and the anatomy of the louse respiratory system suggest this is unlikely.

RESULTS

Observation over several hours of lice treated using 4% high molecular weight dimeticone in a volatile silicone base showed that, although rapidly immobilised initially, the insects still exhibited small movements of extremities and death was delayed. One common effect of treatment is inhibition of the louse's ability to excrete water by transpiration through the spiracles. Inability to excrete water that is ingested as part of the louse blood meal appears to subject the louse gut to osmotic stress resulting in rupture. Scanning electron microscopy coupled with X-ray microanalysis to detect silicon showed dimeticone lotion is deposited in the spiracles and distal region of the tracheae of lice and in some cases blocks the lumen or opening entirely.

CONCLUSION

This work raises doubts that lice treated using dimeticone preparations die from anoxia despite blockage of the outer respiratory tract because movements can be observed for hours after exposure. However, the blockage inhibits water excretion, which causes physiological stress that leads to death either through prolonged immobilisation or, in some cases, disruption of internal organs such as the gut.

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  • Authors+Show Affiliations

    Medical Entomology Centre, Insect Research & Development Limited, 6 Quy Court, Colliers Lane, Stow-cum-Quy, Cambridge, UK. ian@insectresearch.com

    Source

    BMC pharmacology 9: 2009 pg 3

    MeSH

    Animals
    Body Water
    Dimethylpolysiloxanes
    Gastrointestinal Tract
    Pediculus
    Respiratory System
    Silicon
    Stress, Physiological
    Tissue Distribution

    Pub Type(s)

    Journal Article
    Research Support, Non-U.S. Gov't

    Language

    eng

    PubMed ID

    19232080

    Citation

    TY - JOUR T1 - The mode of action of dimeticone 4% lotion against head lice, Pediculus capitis. A1 - Burgess,Ian F, Y1 - 2009/02/20/ PY - 2008/11/20/received PY - 2009/2/20/accepted PY - 2009/2/20/aheadofprint PY - 2009/2/24/entrez PY - 2009/2/24/pubmed PY - 2009/4/22/medline SP - 3 EP - 3 JF - BMC pharmacology JO - BMC Pharmacol. VL - 9 N2 - BACKGROUND: Treatment of head lice using physically acting preparations based on silicones is currently replacing insecticide use due to widespread resistance to neurotoxic agents. It has been postulated that some products act by asphyxiation, although the limited experimental evidence and the anatomy of the louse respiratory system suggest this is unlikely. RESULTS: Observation over several hours of lice treated using 4% high molecular weight dimeticone in a volatile silicone base showed that, although rapidly immobilised initially, the insects still exhibited small movements of extremities and death was delayed. One common effect of treatment is inhibition of the louse's ability to excrete water by transpiration through the spiracles. Inability to excrete water that is ingested as part of the louse blood meal appears to subject the louse gut to osmotic stress resulting in rupture. Scanning electron microscopy coupled with X-ray microanalysis to detect silicon showed dimeticone lotion is deposited in the spiracles and distal region of the tracheae of lice and in some cases blocks the lumen or opening entirely. CONCLUSION: This work raises doubts that lice treated using dimeticone preparations die from anoxia despite blockage of the outer respiratory tract because movements can be observed for hours after exposure. However, the blockage inhibits water excretion, which causes physiological stress that leads to death either through prolonged immobilisation or, in some cases, disruption of internal organs such as the gut. SN - 1471-2210 UR - https://www.unboundmedicine.com/medline/citation/19232080/The_mode_of_action_of_dimeticone_4_lotion_against_head_lice_Pediculus_capitis_ L2 - http://www.biomedcentral.com/1471-2210/9/3 ER -