Efficacy of Oral Ivermectin in Treating Patients With Scabies

Scabies is recognized as a neglected tropical disease (NTD) by the World Health Organisation (WHO), and it reaches epidemic levels of infestation in several resource-limited settings. In such environments, ivermectin is given to whole communities (so-called mass drug administration [MDA]), regardless of whether individuals have signs or symptoms of scabies. A review of MDA efficacy includes seven studies, in which single-dose ivermectin was used, and reports a relative reduction in scabies prevalence in the communities treated, ranging from 31% to 99.9%.¹ With the convenience of single dosing being a major driver, evidence which disputes this as a reasonable strategy is important to review. This brief observational research report describes how, following a single dose of ivermectin for scabies, as approved by the Italian licensing system, 42% of 71 scabies cases treated had persistent infestation when reviewed a month after therapy.² This compared poorly with a previously published series of patients from the same group, wherein just 2% of a group of 68 failed therapy after receiving double-dose oral ivermectin a week apart. Those in the double-dose group had all previously failed to clear on topical anti-scabetic treatment. The ivermectin dose and additional management approaches were identical with the provision of written advice, including environment management recommendations. Single-dose ivermectin treatment is approved in a number of countries, with the advantage of being convenient. Single dose is directly at odds with the 2017 European Guideline on Management of Scabies, which advocates two doses a week apart, recognizing that ivermectin is not ovicidal, and so the second dose is required to deal with mites hatching from the eggs persisting after the first treatment.³ The concern expressed by the authors is that extensive use of single-dose ivermectin may lead to widespread treatment failure and the emergence of resistance. This short report suggests that further work is needed to address the efficacy of single-dose ivermectin for scabies in a robust and randomized way and to clarify whether the recommendations will vary in the intervention setting. Perhaps, it may continue to be expedient in community outbreaks where MDA is to be administered. Prioritizing this research gap should be considered by the International Alliance for the Control of Scabies.⁴

References

1. Rinaldi G, Porter K. Mass drug administration for endemic scabies: a systematic review. Trop Dis Travel Med Vaccines. 2021;7(1):21. https://tdtmvjournal.biomedcentral.com/articles/10.1186/s40794-021-00143-5 
2. Balestri R, Magnano M, Infusino SD, et al. Oral ivermectin to treat scabies: a comparison of two different regimens. Clin Exp Dermatol. 2023;48(3):232-234. https://academic.oup.com/ced/article-abstract/48/3/232/6887191?redirectedFrom=fulltext&login=false 
3. Salavastru CM, Chosidow O, Boffa MJ, et al. European guideline for the management of scabies. J Eur Acad Dermatol Venereol. 2017;31(8):1248-1253. https://onlinelibrary.wiley.com/doi/10.1111/jdv.14351 
4. The International Alliance for the Control of Scabies. Accessed April 12, 2023. https://www.controlscabies.org/