In November of last year, I wrote about the bed bug outbreak which was due to a combination of resurgence in travel after the pandemic together with widespread bed bug resistance to pesticides.
It seems that another mite has also developed resistance to conventional treatment. I only write of it as my eldest is leaving for university later this year. As dermatologists, we tend to see crops of young people in the winter months, often from university halls of residence or rented student accommodation presenting with widespread itchy eruptions which, sometimes after a rather convoluted pathway, end up being diagnosed as having scabies. Needless to say, after being told this, my oldest child was not best pleased.
I think he would be even less pleased if I were to reveal to him that the incidence of scabies is on the rise and that the conventional treatments for scabies, so called scabicides such as permethrin 5% are showing reduced efficacy. This could be due to either resistance or a reduction in sensitivity of the scabies mite to permethrin.
However, on a positive note, there was a paper published in the April edition of the British Journal of Dermatology comparing benzyl benzoate 25% with topical permethrin 5% which showed encouraging results.
[Meyersburg D, Hoellwerth M, Brandlmaier M et al. Comparison of topical permethrin 5% vs. benzyl benzoate 25% treatment in scabies: a double-blinded randomized controlled trial. Br J Dermatol 2024;190:486-491.]
What was the study design?
110 patients aged over 12y of age presenting to Dermatology with a dermatological diagnosis of scabies were enrolled between September 2022 and June 2023. The patients were randomized into two equally sized groups in a double-blinded manner.
All patients received three 60g unlabelled jars containing either permethrin 5% cream or benzyl benzoate 25% emulsion for daily application over three consecutive days. All study participants received verbal and written instructions on the correct application technique together with hygiene measures.
After 3-4 weeks, the patients were re-evaluated of the presence or absence of mites on dermoscopy and then were phoned up 4-8 weeks later to assess if there was any recurrence of itch or rash.
What did they find?
They found that the cure rate in the permethrin group was 27% whereas in the benzyl benzoate group, the cure rate was 87%, a difference that is statistically significant.
What is benzyl benzoate?
Benzyl benzoate has been around for a long time, even before permethrin and other scabicides such as oral ivermectin. It is present in many asthma drugs, has been widely used in veterinary medicine, and is also present in Balsam of Peru and certain flowers such as hyacinths. We’re not sure how it works.
Are there any side effects?
It can be a skin irritant and some people may be allergic to it. It is also not advised to be used in children.
So should we be using it instead of permethrin?
Well, there has been some criticism that if permethrin is applied correctly then it is effective. The British Association of Dermatologists wrote a consensus update on scabies management in October 2023 emphasising the importance of correctly diagnosing, treating and treating contacts with the infected individual.
Permethrin should be applied in two treatments 7 days apart. However, even with written information on how to apply topical treatments properly, it has been shown that 2-30% of the skin surface is left untreated by patients, usually around the ankles and between the toes ie places where the scabies mite prefers to live.
Benzyl benzoate, which is applied for multiple days in a row may be more forgiving of errors which may explain some of its superiority in clearing patients.
In conclusion…
Scabies was identified as a neglected tropical disease by the World Health Organization in 2017 and has been integrated into the WHO Sustainable Development Goals 2021-30. As a practising dermatologist, we are seeing more cases which require more than just standard treatment so anything that works will be welcome!
Kind regards,
Sandy
Dr Sandy Flann, Consultant Dermatologist.
