Scabies is a contagious parasitic infection caused by infestation of the Sarcoptes scabiei var hominis mite. The resulting dermatologic lesions produce moderate to severe pruritus. Epidemics may affect all persons living in close quarters. Standard therapy consists of application of topical acaricides (lindane, permethrin, benzyl benzoate, etc.) that must remain on the affected areas for a certain time and then be washed off. Multiple treatment over the entire body surface may be required. It may be difficult to comply with these requirements in large institutions or in areas where access to a water supply is limited. Ivermectin is an antihelmintic agent used to control onchocerciasis and other parasitoses in humans and has been used for treatment of scabies in animals. Data from several clinical trials have suggested that it may be effective in humans.

Chouela and associates compared the efficacy and safety of ivermectin with that of lindane in the treatment of human scabies. Fifty-three patients with scabies were randomized to receive a single oral dose of ivermectin (150 to 200 µg per kg in 6-mg tablets) and a placebo topical solution, 60 mL, or a single dose of 1 percent lindane topical solution, 60 mL, and placebo tablets. Patients were examined on days 8, 15, 22 and 29. Clinical cure was defined as absence of pruritus and clinical lesions or reduction in symptoms 15 days after the initial treatment or 15 days after the second dose.

Slightly more patients dropped out of the group receiving ivermectin (7 out of 26 patients) than the group receiving lindane (3 out of 27 patients). It was not possible to determine if patients dropped out because treatment was perceived as ineffective or because a cure was achieved and the patients did not return for follow-up examination. Among those patients who did return for follow-up examination, the group treated with ivermectin showed a slightly more favorable healing of the lesions 15 days after initial administration of therapy than the group treated with lindane.

Five patients in the ivermectin-treated group and 11 in the lindane-treated group required a second dose. Patients requiring a second dose in each treatment group had more severe scabies. Only six patients who had severe scabies did not require a second treatment.

The overall assessment of treatment efficacy at day 29 indicated that 18 of the 19 patients in the ivermectin-treated group and 23 of the 24 patients in the lindane-treated group had healing of scabies. This difference was not significant. Adverse effects were mild and transient in both treatment groups. The lindane-treated group had a higher rate of headaches; the ivermectin-treated group had more hypotension, abdominal pain and vomiting. No differences in laboratory test results were evident between the groups.

Clinical symptoms and signs of scabies were still evident in one group of patients 15 days after receiving the first dose of ivermectin, and this group required a second dose. However, these results depended on the severity of the initial lesions. Both treatment groups required a second dose if the initial lesions and symptoms of pruritus were classified as severe.

The authors conclude that oral ivermectin is as effective as topical lindane for the treatment of human scabies. Avoiding the need to apply lindane over large body areas and obviating the requirement to wash off the topical solution after a certain time makes oral ivermectin an effective and easily administered therapy for confined populations where compliance may be compromised.