Does dimeticone clear head lice?
Drug Ther Bull 2007 45(7): 52-55
Our summary and comments
This review, published in July 2007 in the Drug & Therapeutics Bulletin (DTB) examines the supporting evidence for the product Hedrin®, a lotion containing 4% dimeticone (a silicone) launched in 2006. The product is evaluated within the context of supporting evidence for current treatments for head lice. (1) Products now available in the UK are listed according to the March 2007 Medicines and Healthcare products Regulatory Agency (MHRA) classification into medicinal products or medical devices. (2)
Confirmation of infestation
The authors state that head louse eggs take around 7 days to hatch and lice move from person to person via head-to-head contact. Active infestation should always be confirmed by isolating at least one live louse. Combing with a specially designed plastic detection comb is more effective than visual inspection. Many combs sold for this purpose are unsuitable. The best known appropriate comb is the Bug Buster® designed for wet combing with conditioner.
Conventional neuro-toxic insecticide preparations (containing malathion, carbaryl, phenothrin or permethrin) and dimeticone lotion are licensed medicines. With the exception of carbaryl medicines, which are prescription only (POM) for safety reasons, medicines for head lice can be purchased ‘over-the-counter’ (OTC) in pharmacies (P products), but not ‘off-the-shelf’ in general stores.
Medical devices are divided into two groups, combs and fluids. They must be marked CE, and may be sold in general stores as well as pharmacies. Combs include plastic ones designed for the removal of head lice, and metal ones intended for removing louse eggs and nits (empty eggshells). Fluids were originally designed for use as combing aids, but can now “be marketed for use in their own right, provided their activity against head lice is due to physical means (e.g. by asphyxiation) rather than by chemical properties.” (1 p 53).
Evidence of effectiveness
In the DTB review the evidence reported in randomised trials is examined.
The instructions of all neuro-toxic insecticide lotions (in either an aqueous or alcohol base) and permethrin crème rinse state that a single application will eliminate lice and their eggs. However, many trials quoted in the DBT review tested double dosing, an unlicensed use (British National Formulary, 54, September 2007). The authors found a cure rate for two overnight applications a week apart, for malathion lotion of 78% (UK, 2000) (3) and for phenothrin lotion of 75% (UK, 2005) (4). Although included in the list of references, the authors have not noted that another trial of two 2 hour applications of phenothrin lotion a week apart reported a lower 13% cure rate (UK, 2001). (5) The DBT authors consider that the stipulated 10 minute contact time for permethrin crème rinse is insufficient to kill louse eggs. The only trial of permethrin carried out in the UK was of a single application (2005). This trial also tested a single overnight application of malathion lotion. Parents followed the manufactured product instructions and the outcome was assessed by researchers who did not know which product had been allocated. The cure rates at 5 days were 10% for permethrin and 17% for malathion. (6)
Dimeticone, in the solvent, cyclomethicone, another silicone, is thought to kill lice with a physical mode of action by disrupting their ability to manage internal water. It does not kill louse eggs with certainty. The licensed use of dimeticone lotion is for two or more 8 hour or overnight applications a week apart. The one randomised controlled trial was designed to determine whether it had an equivalent efficacy to two applications of aqueous phenothrin (UK, 2005). (4) The trial investigators applied the products. The outcome was assessed by investigators blinded to the treatment allocation. The cure rate at 15 days for two applications of dimeticone lotion was 70%. (4)
On medical devices, whether combs or fluids, the only published randomised trials found by the authors of the DBT review related to the Bug Buster Kit. Use of the 1996 model produced a 38% cure rate (UK, 2000). (3) When nurses used the current 1998 model with an improved Bug Buster comb, a 53% cure rate was found at 14 days (UK, 2001). (5) When parents followed the 1998 model instructions and the outcome was assessed by researchers who did not know whether a Bug Buster Kit or insecticide product had been used, a 57% cure rate was found at 15 days (UK, 2005). (6).
Fluids listed in the DTB review as unsupported by published randomised trials of effectiveness include Full Marks® solution (cyclomethicone with isopropyl myristate, a fatty acid ester) and Lyclear® Spray Away, Nice ‘n’ Clear® Lotion and Nitty Gritty Solution, which contain essential plant oils.
Evidence of unwanted effects
Dimeticone lotion caused fewer irritant reactions (2.4%) than phenothrin (8.8%). (4) Unlike neuro-toxic insecticides and essential oils, it is not absorbed through the skin. Insecticide resistance levels in UK lice to neuro-toxic insecticides of between 82% (7) and 90% (6) have been reported for permethrin, and between 22% (3) and 64% (7) for malathion. As the action of silicone on lice is not chemical, resistance is unlikely to develop.
It is recommended practice to coat the scalp and the length of the hair with a formulated treatment and the quantity required varies with hair type and length. The cost to the NHS of prescribing 50 ml of dimeticone is around £3.00, whereas 50 ml of conventional insecticide is about £2.00 and a Bug Buster Kit is about £4.00. The general public purchasing OTC pay roughly double these prices.
The review concludes that although 4% dimeticone lotion has only been compared to 0.5% phenothrin aqueous liquid, it is reasonable to regard it as a “first line alternative” to the conventional insecticides, particularly for those who do not wish to use the latter. There are no long-term data and no direct comparison with Bug Busting® (regarded as comparatively time-consuming by the authors). Use of the Bug Buster Kit appears to be “somewhat less effective” than “chemicals”, but may be preferred by people wishing to avoid them.
This review confirms that no formulated product for head lice, applied according to the instructions, can guarantee eradication of an infestation. However, by stating vaguely that louse eggs take around 7 days to hatch, the authors fail to address one major reason for this, namely that the incubation range is 6-11 days. (8) To protect users from being taken unawares by lice continuing to hatch, product instruction sheets should contain the correct advice on checking outcomes thoroughly, as in the leaflet NHS: Prevention and treatment of head lice. (9) Fulfilling this requirement casts a new light on the comparative convenience and cost of the Bug Buster Kit. One purchase of a Bug Buster Kit serves a whole family for detection and cure, a fact that the authors do not mention. (10) During treatment the user learns how to recognize any new incoming lice. No lotion can tell the user if the patient has caught more egg-laying lice between doses. Moreover, checking that a head is clear after using the Kit for eradication, is an integral part of the Bug Busting method.
A team from our charity, Community Hygiene Concern, led a review of studies using the Bug Busting approach, carried out in the UK, Belgium and Denmark since 1996. (11) In Chester (UK) parents were given a choice of using the Bug Buster Kit alone, or a prescription for two applications of conventional insecticide followed by assessment with a Bug Buster Kit. The local primary care trust saw a 24 per cent reduction in prescribing costs for treatment of head lice between April 2004 and March 2005 and local healthcare staff reported spending less time advising parents. (11)
Primary care trusts which limit the choice to dimeticone or conventional insecticide, and do not introduce the Bug Buster Kit for outcome assessment, will not benefit from these cost savings.
Note on the Medicines and Healthcare products Regulatory Agency (MHRA) marketing authorisations: The MHRA classifies formulated treatments for head lice and fine-tooth combs as medicinal products or medical devices. (2) The claims made for medicinal products are assessed as part of their application for a licence. For medical devices, the MHRA does not “investigate the truth or validity of any claims being made for the product”. (2, p 12)
Last updated 01/10/2007
- Anon Does dimeticone clear head lice? Drug Ther Bull 2007 45: 52-55 The full text is available via Infotrieve here
- Medicines Borderline Section, Medicines and Healthcare products Regulatory Agency. A Guide to what is a medicinal product. MHRA Guidance Note No. 8. Revised March 2007, London, MHRA 47pp (1-21, plus 30-5 Appendix 3 Head lice products)
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- Hill et al. (2005) Single blind, randomised, comparative study of the Bug Buster kit and over the counter pediculicide treatments against head lice in the United Kingdom. British Medical Journal 331: 384-7.
- Downs et al. (1999) Evidence for double resistance to permethrin and malathion in head lice. British Journal of Dermatology 141: 508-11.
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- Ibarra J, Fry F, Wickenden C, Olsen A, Vander Stichele R, Lapeere H, Jenner M, Franks A, Smith JL. Overcoming health inequalities by using the Bug Busting ‘whole-school approach’ to eradicate head lice. Journal of Clinical Nursing 2007; 16: 1955-1965 highwire.stanford.edu/cgi/medline/pmid;17880484
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