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Scabies is a major global health problem caused by the mite Sarcoptes scabiei var. hominis, an obligate human ectoparasite measuring between 330 and 450 µm in length. Treatment of this disease has undergone various changes from the days of Roman physician Celsus, when sulphur mixed with liquid pitch was used as a primary approach.
Today, scabies therapy involves making the precise diagnosis, identifying the correct clinical context to guide treatment of contacts and fomites, selecting the most effective medication, understanding how to use the agent appropriately, and following a rational basis for when to use and reuse a drug of choice. Scabicidal drugs can be broadly divided into topical agents and oral agents.
The mainstay of scabies treatment are topical scabicidal agents. Permethrin 5% cream is currently accepted as the gold standard because of an efficacy greater than 90% and excellent safety profile. This topical drug is labeled for application to the entire body for 8 to 12 hours, usually right before bedtime.
Lindane 1% cream or lotion (also known as gamma benzene hexachloride) has been found to be very effective alternative option in the treatment of this ectoparasitosis. Nevertheless, its potential neurotoxicity (especially with repeated applications) has limited its use, thus the product is no longer available in certain countries.
Benzyl benzoate, an ester of benzoic acid and benzyl alcohol, is neurotoxic to the mites and used as a 25% emulsion for the contact period of 24 hours. As it is very effective when used properly, the emulsion should be applied below the neck three times within 24 hours without an intervening bath. Its use increased for the treatment of permethrin-resistant crusted scabies.
Crotamiton is used as 10% cream or lotion with the success rate between 50% and 70%, which is a significantly less effective than permethrin. Although this topical agent is labeled for application over 1 to 2 days, daily application for 5 days has yielded improved cure rates.
The effectiveness of malathion 0.5% lotion has been demonstrated by several small studies, with cure rates ranging from 83% to 100%. It is appropriate for the treatment of hairy areas of the body (such as the scalp) and requires two applications 7 days apart.
As increasing resistance to scabies treatments may be on the horizon, standard of care should encompass routine treatment of the scalp and face and re-treatment of patients at day 4 (based the scabies life cycle) in order to guarantee more efficient mite eradication. Furthermore, practitioners should attempt to treat all close contacts concurrently with the source patient.
Oral Ivermectin, a drug originally used in humans to control outbreaks of onchocerciasis in Africa and Latin America, can now be used as an off label oral medication for scabies (alone or in combination with a topical agent). Most studies have shown that one or two doses of Ivermectin (200 µg per kilogram of body weight) result in cure rates equivalent to treatment with conventional topical medications.
Efficacy rates from open-label studies of Ivermectin for the treatment of classic scabies range from 76% to 100%. Safety profile of the drug is also considered good, as no serious adverse effects were noted in the treatment of large number children with scabies in the Solomon Islands.
There is some observational evidence of Ivermectin effectiveness in controlling scabies outbreaks in institutional settings such as nursing homes. Mass drug administration programs have been attempted to use this agent for scabies control in endemic communities around the world; however, such programs’ superiority over alternative topical treatment is questionable.
Populations must be educated and sensitized on related preventive measures such as adoption of rigorous personal hygiene, avoidance of overcrowding and overpopulation in rooms and houses whenever possible, as well as the promotion or reinforcement of hand hygiene.