Scabies: Molecular Perspectives and Therapeutic Implications in the Face of Emerging Drug Resistance

Kate E. Mounsey; Deborah C. Holt; James McCarthy; Bart J. Currie; Shelley F. Walton

Disclosures

Future Microbiol. 2008;3(1):57-66. 

In This Article

Treatment of Scabies: Present & Future

It is critical that both the patient and their potential contacts are treated adequately, regardless of the acaricide used. Topical acaricides need to be applied to the entire body, including under the nails, and left on the skin for the recommended time. Additionally, because no acaricide has been confirmed to have ovicidal properties, retreatment may be necessary in some cases to kill newly hatched mites. As clinical symptoms are complicated by delayed onset of up to 6 weeks following the establishment of infection, a frequent cause of recurring scabies is reinfestation from untreated contacts. Therefore, it is essential that contacts are treated regardless of symptoms.

In developing regions of the world, cost and availability of the acaricide are of obvious importance when selecting the most appropriate treatment for scabies. Ideally, the acaricide should be easy to apply, minimally absorbed through the skin, nontoxic for the host, effective against both mites and eggs, and effective as a single-dose regimen. However, from the most widely used treatments ( Table 1 ), no drug currently fulfils all these criteria.

Although crotamiton is currently recommended in northern Australia for treating babies less than 2 months of age,[6] low efficacy has been reported in clinical trials.[7,8] This raises the issue of whether crotamiton is appropriate for controlling infant scabies in the community setting, especially considering the high burden of scabies in this group.[9] Recent studies by our laboratory, however, now confirm that 10% crotamiton has potent acaricidal properties in vitro (Figure 1). These results support the rationale for further exploration of crotamiton as an acaricide, possibly looking at different treatment regimes, alternative formulations to improve bioavailability or even its incorporation into combined treatment strategies.

Figure 1.

In vitro sensitivity of Sarcoptes scabiei var. hominis mites to routinely used acaricides in northern Australia.

While benzyl benzoate is highly efficacious in vivo and in vitro, treatment guidelines for this drug vary, with some recommending three applications within 24 h.[10] Given its potency and propensity to cause significant skin irritation, this regimen may be excessive. Nevertheless, since this is one of the few acaricides where resistance has not been described, its use today remains relevant.

Permethrin has replaced lindane as the first-line treatment for scabies in Australia, the UK and the USA.[11] It has also been implemented for community mass treatment of scabies in Panama and Australia.[3,4,12] One of the few caveats of permethrin is that it is the most expensive topical acaricide, a consideration that restricts its use in developing regions.

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