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Head lice head to head: dimeticone versus malathion

Peter Burrill
BPharm(Hons) MRPharmS DipPresSci FCPP FFPMM
Specialist Pharmaceutical Adviser for Public Health
Derbyshire County PCT

A trial compared the recently-introduced 4% dimeticone lotion (Hedrin; Thornton and Ross) with 0.5% malathion liquid (Derbac-M liquid; SSL).1 A previous study had shown that Hedrin was equivalent in activity to 0.5% phenothrin liquid.2

Method
Participants were recruited via local newspaper and radio advertising. Families responding were sent a Participant Information Booklet by post. Those who then wished to enrol telephoned again to request a home visit, usually within 24 hours. Trained investigators used a standard protocol to examine participants for head lice using a plastic detection comb. If lice were found, and the participant was eligible, a signed consent and assent procedure was followed. Other household members were offered examination and invited to join if eligible.

The lower age limit was six months in conformity with the licence for both products; there was no upper limit.
Treatments and assessments were conducted in the home. No payment was offered for participation. Ineligible infested household members were provided with 4% dimeticone lotion. Participants were required to confirm their availability for the duration of the study (14 days following the first treatment) in order to be included in the study.

Dimeticone 4% lotion was supplied in 150 ml bottles (Hedrin 4% lotion) and 0.5% malathion liquid in 200 ml bottles (Derbac-M liquid). Both products were applied to dry hair, using enough to thoroughly moisten the hair and scalp. Investigators applied the products evenly through the hair using their fingers.

Treatments were applied to the full hair length and left to dry naturally. The same regimen was repeated seven days later.
Participants were provided with nonmedicated, conditioner-free shampoo to ensure all treatments were washed off using the same preparation. Carers were advised of the earliest time treatment should be removed, usually the following morning, and asked not to use louse combs, other forms of head louse treatment during participation, and not to divulge the treatment to assessors to maintain blinding. Most participants had previously used one or both preparations so it was impossible to blind them to treatment.

The primary outcome was elimination of head lice using two applications of treatment. Cure was defined as no lice after the second application of treatment, on days 9 and 14.
A sample size calculation was done and sufficient patients enrolled. The trial was allocation concealed. Investigators blinded to allocation performed the assessments. Intention-to-treat analysis was carried out.

Results
Fifty-eight children aged 1-13 and 15 adults from 32 families participated (73 people) and received dimeticone lotion (43) or malathion liquid (30). A total of 68 (93.2%) participants (39 dimeticone, 29 malathion) completed the trial. There were four withdrawals from the dimeticone group: one dropped out after one follow-up for family reasons, as did the single dropout from the malathion group. Three others from the dimeticone group failed to complete the study, not keeping any appointments after the first assessment on day 2. These were treated as cases lost to follow-up. All other participants had complete data sets with two treatments given seven days apart and post-treatment assessments conducted on days 2, 6, 9, and 14 after the first treatment.

There was no significant difference between the groups in respect of age, gender, intensity of infestation, hair length, thickness (density), degree of curl, or whether dry/greasy.
Post-treatment examinations found 25 cures and five cases of reinfestation after cure with dimeticone and nine and one respectively for malathion. If the five dropouts were taken as treatment failures (worst case analysis) the data provided positive outcomes of 30/43 (69.8%) for dimeticone and 10/30 (33.3%) for malathion with a significant difference of 36.4% (14.7% to 58.2%, p 

The advantage of dimeticone over malathion was found in all the data subgroups analysed (apart from those experiencing adverse events). The most marked difference between the treatments was for participants with thick hair, where the rate of cure was only 1/7 (14.3%) for 0.5% malathion liquid as against 11/11 (100.0%) for 4% dimeticone lotion (p

Questionnaires showed investigators rated dimeticone easier to apply, and easier and quicker to work into the hair. The participants rated the products feeling similar after application, but dimeticone as less odorous, easier to wash out and leaving the hair feeling softer when dried. Both products were nonirritant to the carers' hands and generally left the hair easy to comb. Those given dimeticone were significantly more inclined to use the product again than those using malathion (97% vs 31%).

The safety evaluation found five adverse events in 43 participants using dimeticone and nine in 30 people using malathion. There were no serious adverse events.

Discussion

  • This is the second study to show the effectiveness of 4% dimeticone lotion in treating head louse infestation.
  • Dimeticone was significantly better than malathion (NNT of 2-3).
  • As investigators applied the products these results represent correct use. Cure rates may be lower in real-life situations where parents apply the products and may not be so diligent.

The authors conclude that dimeticone lotion is likely to prove more reliably effective than malathion products in current consumer use. So should 4% dimeticone lotion now be our firstline recommendation? This seems a reasonable conclusion.

References
1. Burgess IF, Lee PN, Matlock G. Randomised, controlled, assessor blind trial comparing 4%
dimeticone lotion with 0.5% malathion liquid for head louse infestation. PLoS ONE 2007; 2(ii):e1127.doi:10.1371/journal.pone.0001127
2. Burgess IF, Brown CM, Lee PN. Treatment of head louse infestation with 4% dimeticone lotion: randomised controlled equivalence trial. BMJ 2005;330:1423-6.