Medication Summary
The mainstay of scabies treatment is the application of topical scabicidal agents, with repeat application in 7 days. The treatment of choice is permethrin 5% lotion. A 2007 Cochrane Review found that topical permethrin appeared to be the most effective treatment for scabies. [69] Alternative drug therapy includes precipitated sulfur 6% in petrolatum, lindane, benzyl benzoate, crotamiton, and ivermectin; a possible new option is albendazole. [70, 71, 72, 73] Regarding ivermectin, a second course of treatment is often recommended 7-10 days later because of some developing larvae that may survive the initial treatment. [74]
Pruritus can be treated with an oral antihistamine, such as hydroxyzine hydrochloride (Atarax), diphenhydramine hydrochloride (Benadryl), or cyproheptadine hydrochloride (Periactin). More severe symptoms may require a short course of topical or oral steroids.
Secondary infections may require antibiotics, which should be prescribed based on culture and sensitivity data.
Scabies outbreaks in nursing homes and cases of crusted scabies may require combination therapy consisting of topical application of permethrin and 2 oral doses of ivermectin at 200 μg/kg (administered 1 wk apart). [75] Bullous scabies may respond to ivermectin therapy. [76]
Observations, however, have noted emerging drug resistance to oral ivermectin and 5% permethrin. [77] Drug resistance is emerging as a concern with repeated administration. Clinical resistance has not been documented for permethrin use, but it has been documented in 2 people with crusted scabies who had repeated regimens of multiple doses of ivermectin. [7] Thus, the need to define molecular mechanisms of drug resistance in scabies mites is urgent, as is the development and assessment of alternative therapeutic options. [78]
Benzyl benzoate,an ester of benzoic acid and benzyl alcohol, is neurotoxic to mites and has been used. It is not available in the United States [9] and is not FDA approved as a scabicide, although it is used in Europe. [57] There is an unmet need for new acaricide molecules with greater efficacy and improved pharmacological profiles to tackle scabies and its morbidity. One such molecule may be afoxolaner (AFX). It shows efficacy against fleas, ticks, and mites in dogs, as well as scabies. Controlled studies of the efficacy of scabies treatments can be difficult to set up, as scabies mites cannot be maintained or propagated in vitro away from their host for more than a few days. [79]
Antiparasitic Agents
Class Summary
Treatment options include either topical or oral medication. Topical options include permethrin cream (drug of choice), lindane, benzyl benzoate, crotamiton lotion and cream, sulfur, topical ivermectin, tea tree oil, or oil of the leaves of Lippia multiflora Moldenke, a shrub found growing in West African savanna. Oral options include ivermectin, although it has not been approved by US Food and Drug Administration (FDA) for the treatment of scabies. A second course of treatment is often recommended 7-10 days later because of some developing larvae that may survive the initial treatment.
The Centers for Disease Control and Prevention (CDC) recommends treatment with either permethrin lindane or ivermectin. Permethrin is the drug of choice in the United States and the United Kingdom, but it is not available in France. In some studies, it has been shown to be more effective than a single dose of oral ivermectin, although it has equivalent efficacy when 2 doses of ivermectin are used at time zero and 2 weeks later. In severe cases, a topical medication may be used with oral medication (ivermectin).
A 2007 Cochrane Review found that topical permethrin appeared to be the most effective treatment for scabies.
Drug resistance is emerging as a concern with repeated administration. Clinical resistance has not been documented for permethrin use, but it has been documented in 2 people with crusted scabies who had repeated regimens of multiple doses of ivermectin.
Permethrin (Acticin, Elimite)
A neurotoxin that causes paralysis and death in ectoparasites, permethrin 5% cream is the drug of choice for scabies treatment, especially in infants over age 2 months and small children. It is more effective than crotamiton in treating symptoms and reducing chances of secondary bacterial infection.
The lotion should be applied over the entire body, including the face and scalp in infants. It should be left on for 8-12 hours and then rinsed. Reapplication 1 week later is advised; however, no controlled studies have demonstrated that 2 applications are more effective than 1.
Lindane
This is available in 1% lotion or cream. Lindane stimulates the nervous system of parasites, causing seizures and death. It was previously the standard treatment for scabies but is now considered a second-line drug, to be used if other agents fail or are not tolerated. Lindane is not safe in children or neonates, because of increased transcutaneous absorption leading to possible neurotoxicity. The systemic absorption rate of lindane is 10 times greater than that of permethrin, and its serum levels are more than 40 times higher. Overall, permethrin is a safer choice.
Sulfur topical (Sulpho-Lac, Sulfo-Lo)
This is the oldest scabicide, although it has not received FDA approval for scabies treatment. Topical sulfur is one of only a few scabicidal agents that can be used safely in very small children (< 2 mo) and in pregnant women. Sulfur is messy, malodorous, stains clothes, and requires repeat applications, thus reducing compliance. Sulfur should be used only when a patient cannot tolerate permethrin, lindane, or ivermectin. It is inexpensive and can be used for mass therapy in resource-poor economies. Creams or ointments ranging from 2-10% (6% preferred) are available.
Crotamiton (Eurax)
Crotamiton is a 10% cream or lotion for the treatment of scabies. Its mechanism of action is unknown, and the drug is associated with frequent treatment failures.
Ivermectin (Stromectol)
Ivermectin binds selectively with glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, causing cell death. It is available in 3- and 6-mg tablets. The drug is currently approved for the treatment of human onchocerciasis and strongyloidiasis. Although it is not approved by the FDA for the treatment of scabies, it is widely administered for this purpose, with the literature supporting its use.
Ivermectin is a synthetic macrocyclic lactone belonging to the avermectin group of antibiotics. It has no antibiotic activity but is active against a number of endoparasites and ectoparasites of humans and animals. Ivermectin is an ideal agent in cases in which topical therapy is difficult or impractical, such as in widespread institutional infestations and bedridden patients. Patients with crusted scabies may require 3 or more doses, given at 1- to 2-week intervals.
Ivermectin is contraindicated in patients with allergic sensitization or nervous system disorders and in women who are pregnant or breastfeeding. Children younger than 5 years or weighing less than 15 kg should not be treated with ivermectin.
One study compared the efficacy of ivermectin with benzyl benzoate lotion in the treatment of scabies and found that ivermectin was at least as effective as the other drug and led to more rapid improvement. The efficacy of benzyl benzoate lotion and permethrin were also evaluated in a retrospective, matched cohort study of pregnant women. No adverse effects on pregnancy outcome were reported in patients using either drug.
Topical Antibiotics
Class Summary
These agents are used to treat secondarily infected lesions.
Mupirocin (Bactroban, Centany)
This agent is used to treat infection with Staphylococcus species, beta-hemolytic streptococci, or Streptococcus pyogenes. It inhibits protein and ribonucleic acid (RNA) synthesis by inactivating transfer-RNA synthetase.
Corticosteroids, Topical
Class Summary
These agents may be applied to help control intense pruritus caused by scabies.
Hydrocortisone, topical (Westcort, U-Cort, Ala Cort, Rederm)
This is an adrenocorticosteroid derivative that is suitable for application to skin or external mucous membranes. It has mineralocorticoid and glucocorticoid effects that result in anti-inflammatory activity. Hydrocortisone is considered the lowest-potency topical steroid.
-
Scabies mite scraped from a burrow (original magnification, 400X).
-
A typical linear burrow on the flexor forearm. Courtesy of Kenneth E. Greer, MD.
-
A subtle linear burrow accompanied by erythematous papules on the sole of the foot in a child with scabies. Courtesy of Kenneth E. Greer, MD.
-
Erythematous papules and papulovesicles on the flexor wrist. Courtesy of Kenneth E. Greer, MD.
-
Scabies on the penile shaft and glans. Courtesy of William D. James, MD.
-
Scabietic papules on the penile shaft and scrotum. Courtesy of Kenneth E. Greer, MD.
-
Widespread eruption on the back of an infant with scabies. Courtesy of Kenneth E. Greer, MD.
-
Nodular scabies in an infant. Courtesy of Kenneth E. Greer, MD.
-
Nodular scabies. Courtesy of Kenneth E. Greer, MD.
-
Crusted scabies. Courtesy of William D. James, MD.
-
Crusted scabies. Courtesy of Kenneth E. Greer, MD.
-
Scabies preparation demonstrating a mite and ova. Courtesy of William D. James, MD.
-
Scabies. Erythematous vesicles and papules are present on torso extremities, some with adjacent linear excoriations.
-
In routine scabies, a single mite is seen. Eosinophilic spongiosis may be present (hematoxylin and eosin; original magnification, 400X).
-
Scabies mite in the stratum corneum. Courtesy of William D. James, MD.
-
In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum. The epidermis is spongiotic (hematoxylin and eosin; original magnification, 100X).
-
Scabies. Courtesy of William D. James, MD.
-
Scabies in the interdigital web spaces. Courtesy of William D. James, MD.
-
Papulovesicles and nodules on the palm in a patient with scabies. Courtesy of Kenneth E. Greer, MD.
-
Scabies on buttocks. Courtesy of William D. James, MD.
-
Scabies on penis. Courtesy of Hon Pak, MD.
