Scabies: Permethrin is not really effective anymore

The standard treatment for scabies is permethrin, but it is becoming less due to mutations in the scabies mite that have led to resistance development.

Scabies mite mutations and consequences for therapy

Why are the mites resistant?

In anthropods, a mutation regularly occurs in voltage-dependent sodium channels, which can lead to resistance. Until now, it was not assumed that this could also occur in the scabies mites. In these pathogens, the change in the sodium channels leads to an exchange of methionine with leucine, which can cause knockdown resistance. In many cases, this results in resistance to permethrin, the drug that is often used to treat the skin disease.

What do the mutations mean for medical practice?

If scabies pathogens are affected by the mutation, treatment with permethrin may be less effective or unsuccessful. This was the case for the majority of patients in the study population. Only around 15% of patients were able to achieve remission with permethrin alone - and often only after an above-average length of treatment.

However, this does not mean that the disease is not treatable. Rather, it means that monotherapy no longer leads to successful treatment in the majority of cases, but that various drugs should be used simultaneously: A combination of permethrin and ivermectin was successful for over 60% of the study participants.

Mutated scabies mites: Key take-away

In the treatment of scabies, combination therapy or prolonged permethrin administration may make sense. In an increasing number of cases, resistance to the usual dosage of permethrin is to be expected. Not all patients achieve the desired treatment success with the drug. As with many other anthropods, the scabies mite is also affected by mutations that can lead to resistance. The mutated pathogens are expected to spread in the future. These findings should therefore be included in treatment planning.

  1. Riebenbauer K, Purkhauser K, Walochnik J, Urban N, Weber PB, Stamm T, Handisurya A. Detection of a knockdown mutation in the voltage-sensitive sodium channel associated with permethrin tolerance in Sarcoptes scabiei var. hominis mites. J Eur Acad Dermatol Venereol. 2023 Nov;37(11):2355-2361. doi: 10.1111/jdv.19288. Epub 2023 Jul 10. PMID: 37356045.