Advice
Intervention and alternatives
Ivermectin is an anthelmintic that acts against infections caused by parasitic worms (helminths). It also appears to be effective against other endoparasites and ectoparasites.
Oral ivermectin is licensed in the USA (Stromectol) for the treatment of strongyloidiasis and onchocerciasis (river blindness) parasitic infections, and in France for the treatment of strongyloidiasis and scabies (see Welsh Medicines Information Centre 2012) It is available on a named-patient basis in the UK from 'special order' manufacturers or specialist importing companies (see British National Formulary 2014). Oral ivermectin has been used to treat crusted scabies (also known as hyperkeratotic, Norwegian or atypical scabies) that does not respond to topical treatment alone. It has also been used to treat other forms of 'difficult-to-treat' classical scabies (for example, if a topical treatment cannot be used or has not worked). There are also reports in the literature about using oral ivermectin to treat outbreaks of scabies in mass care settings, such as nursing homes.
The manufacturer of ivermectin has provided a European summary of product characteristics for Stromectol 3 mg tablets (Merck Sharp & Dohme: personal communication December 2013), which states that the recommended dose for scabies is a single oral dose of ivermectin 200 micrograms/kg body weight. For classical scabies, recovery is considered definite only after 4 weeks have elapsed since treatment. Persistence of pruritus or scraping lesions does not justify a second treatment before this date. Administration of a second dose within 2 weeks after the initial dose should only be considered when new specific lesions occur or when parasitological examination is positive. For crusted scabies, a second dose within 8–15 days of the initial dose of ivermectin and/or concomitant topical therapy may be necessary.
Condition
Scabies is a parasitic infection of the skin. It is caused by the Sarcoptes scabiei mite. The female mite burrows into the skin to lay eggs. Larvae emerge from the eggs. These develop through two nymphal stages into adult males and females. It takes 10–13 days for adult mites to appear after eggs have been laid. Female mites make new burrows, and male mites move actively between burrows seeking to mate with females.
Scabies is recognised by a delayed hypersensitivity reaction to the saliva and faecal material excreted by the mite. It causes intense itching, particularly at night, with eruptions on the skin. The classical sites of infestation are between the fingers, the wrists, axillary areas, female breasts (particularly the skin of the nipples), peri-umbilical area, penis, scrotum and buttocks.
The infection usually spreads from person to person via direct skin contact. Transfer via inanimate objects such as clothing or furnishings is possible, although this normally only occurs in cases of crusted scabies.
NICE Clinical Knowledge Summaries (CKS) for scabies recommends that people with scabies and all members of their household, close contacts and sexual contacts need to be treated at the same time (within a 24-hour period), even if they do not have symptoms of scabies. Contacts can be treated with topical treatments even if the person with scabies is treated with ivermectin.
Crusted scabies (also known as hyperkeratotic, Norwegian or atypical scabies) is a more severe form of scabies associated with disorders of the immune system (such as HIV infection), reduced ability to scratch (for example, because of physical incapacity or because the itch is not perceived because of skin anaesthesia) and learning difficulties, dementia, or Down's syndrome. Clinically, this atypical form of scabies presents with a hyperkeratotic dermatosis resembling uncomplicated xeroderma or with a granular appearance. Lymphadenopathy and eosinophilia can be present, but itching may be unexpectedly mild. Patients with extensive crusted scabies may harbour millions of mites and are highly infectious. The dermatological distribution of mites in such patients is often atypical (for example, it may include the head), and treatment in hospital is often advised.
Alternative treatment options
NICE Clinical Knowledge Summaries (CKS) for scabies recommends permethrin 5% dermal cream as the first-line treatment for scabies. Malathion 0.5% aqueous liquid can be used if permethrin cream is inappropriate. However, malathion liquid is currently unavailable in the UK.
These topical treatments should be applied to the whole body, with special attention to the areas between the fingers and toes and under the nails. The treatments should be applied twice, with applications 1 week apart. The treatment should be applied for a prolonged period (8–12 hours for permethrin and 24 hours for malathion) before being washed off.
Benzyl benzoate is another topical treatment for scabies, but it is not as effective as permethrin or malathion and is generally no longer used. It is an irritant and should be avoided in children (British National Formulary 2014).