First documentation of in vivo and in vitro ivermectin resistance in Sarcoptes scabiei. Clin Infect Dis

Ivermectin is increasingly being used to treat scabies, especially crusted (Norwegian) scabies. However, treat-ment failures, recrudescence, and reinfection can occur, even after multiple doses. Ivermectin resistance has been documented for some intestinal helminths in animals with intensive ivermectin exposure. Ivermectin resistance has also been induced in arthropods in laboratory experiments but, to date, has not been documented among arthropods in nature. We report clinical and in vitro evidence of ivermectin resistance in 2 patients with multiple recurrences of crusted scabies who had previously received 30 and 58 doses of ivermectin over 4 and 4.5 years, respectively. As predicted, ivermectin resistance in scabies mites can develop after intensive ivermectin use. Ivermectin is increasingly being used to treat scabies, especially in those with hyperinfestation (crusted or Norwegian scabies) [1, 2]. Scabies is endemic in many remote Aboriginal communities in the Northern Ter-ritory of Australia, and a minority of patients develop crusted scabies. Unlike in most reports of crusted sca-bies, the cases we treat in these communities often in