Ivermectin for Scabies


18 March 2003

Dear Editor,

Brooks and Grace1 have shown in Vanuatu that clinical scabies responds better to ivermectin than to topical benzyl benzoate. In Australia, ivermectin can only be used when other treatments fail and then not in children under 5 years of age as safety has not been established in this group. Scabies is still a problem in some Australian children.

In a Queensland Aboriginal Community almost all medical care is given by the local hospital. We have records for all visits to the hospital outpatients clinics and emergency services for 1993−1996 and 1998−2001. During these years there were 104 959 visits, with 13 390 being children under 5 years. In 3169 of all visits, the diagnosis was scabies (3.0% of all visits) and scabies was diagnosed in 834 of the 13 390 visits of under-fives (6.2%). Four hundred and twenty-nine children under the age of 5 years were involved, 42 made 5−10 visits and 20 made more than 10 visits. Over 70% of those with scabies had secondary bacterial infection. Most cultures from these lesions grew streptococci and staphylococci.

Local dressings and systemic antibiotics were used for secondary infection. Children with large infected areas were admitted. These children had urine samples sent to the laboratory and many had microscopic haematuria. The combination of streptococcal infection and haematuria suggests subclinical glomerulonephritis. Although the haematuria cleared, the underlying damage could be the starting point for progressive renal damage and end-stage renal failure. There were no clinical cases of rheumatic fever.

Local scabicides can be used only after the secondary infection has cleared and often give only temporary benefit. Benzyl benzoate stings ulcerated areas, permethrin is safe and about 90% effective when properly used simultaneously by all members of the family and other contacts. However, recurrence of scabies is common either from improper use of permethrin within the family or from external reinfection. A single oral dose of ivermectin can be given to all family members (over the age of 5 years under present rules) at any time and gives a 70% cure rate. A second dose a week later gives 90% cure rate3,4.

Any effective therapy that can be given orally to all members of the family at the time of initial contact has obvious advantages for clinical medicine and for public health. Oral ivermectin has been widely used with excellent clinical benefits and few reports of drug-related problems. The caveat on its use for children in Australia does not relate to known harm, but to lack of evidence for safety. The dictum primum-non-nocere (first do no harm) holds but we must also consider the risk/benefit ratio. The evidence for risk of ivermectin in children is weak. The evidence for immediate harm of scabies is strong and the long-term effects of secondary streptococcal infection are well known. Ivermectin has many practical advantages over topical therapy. The Australian Pharmaceutical Advisory Board might consider making ivermectin the preferred treatment for scabies in patients of all ages. This should reduce the risk of long-term renal and cardiac damage in Australians, and particularly Aboriginal people.