Scabies

  • cutaneous infestation caused by the mite Sarcoptes scabiei.
  • characterized by à intensely pruritic eruption with small, often excoriated, erythematous papules in sites such as the fingers, wrists, axillae, areolae, waist, genitalia, and buttocks.
  • Crusted scabies, a less common clinical variant, typically presents with scaly, crusted, fissured plaques and primarily occurs in immunocompromised individuals.

The successful management of scabies involves

  • eradication of mites from the affected person,
  • management of associated symptoms and complications,
  • assessment for additional individuals who may require treatment, and
  • implementation of measures to minimize transmission and recurrence of infestation.

ERADICATION OF INFESTATION

dependent upon the clinical presentation (classic, crusted, or endemic scabies) and patient population

Treatment of both the patient and close personal contacts is suggested to prevent recurrent infestation.

Classic scabies — 

Topical permethrin and oral ivermectin are the most common first-line treatments. Benzyl benzoate, topical sulfur, crotamiton, lindane, and topical ivermectin are examples of other treatments.

First-line therapies — 

Topical permethrin is highly effective for scabies, with cure rates in randomized trials approximating or exceeding 90 percent

Oral ivermectin is an alternative first-line treatment that has the advantages of ease of administration and lower cost.

Permethrin — topical synthetic pyrethroid agent that impairs function of voltage-gated sodium channels in insects, leading to disruption of neurotransmission.

Administration –

Patients should massage permethrin cream thoroughly into the skin from the neck to the soles of the feet, including areas under the fingernails and toenails

Thirty grams is usually sufficient for a single application for an average adult.

In young children, scalp involvement is common. Therefore, permethrin should also be applied to the scalp and face (sparing the eyes and mouth) in this population.

Permethrin should be removed by washing (shower or bath) after 8 to 14 hours.

Treatment is often performed overnight.  

A second application one to two weeks later may be necessary to eliminate mites and is typically performed. However, the relative efficacy of one versus two applications of permethrin has not been studied.

Efficacy –In a systematic review and meta-analysis of randomized trials, topical permethrin and oral ivermectin appeared similarly effective

Adverse effects – Permethrin is generally well tolerated. Skin irritation is a potential side effect.

Oral ivermectin — antiparasitic alternative to permethrin that has the advantage of ease of administration. This mode of treatment may be particularly useful for large scabies outbreaks in nursing homes and other facilities where topical therapy can be impractical.

Oral ivermectin is not a recommended first-line treatment for pregnant or lactating women and children who weigh less than 15 kg.

Administration – Ivermectin therapy for classic scabies consists of a 200 mcg/kg single dose followed by a repeat dose after one to two weeks

Efficacy –In addition, based upon a systematic review and meta-analysis of randomized trials, oral ivermectin appears to be as effective as topical permethrin

Adverse effects –generally well tolerated; most reports of severe adverse effects have occurred in patients with helminthic infections

Other agents — 

Additional topical treatment options for scabies include

  • benzyl benzoate,
  • topical sulfur, 
  • lindane, 
  • crotamiton, and 
  • malathion 

These agents have not been shown to be more effective than topical permethrin 

Topical ivermectin is a newer, albeit high-cost, agent that appears to have efficacy for scabies In an open-label, randomized trial that compared permethrin, topical ivermectin, and oral ivermectin, cure rates for permethrin and topical ivermectin were similar.

Benzyl benzoate (10 or 25%)

commonly used in resource-limited countries because of the drug’s low cost.

Treatment regimens vary; the drug may be applied once daily at night on two consecutive days, with a repeat treatment cycle after seven days

Topical sulfur (6 to 33%)

relatively inexpensive and primarily used for the treatment of neonates and pregnant women. Sulfur ointment is applied overnight for three consecutive days.

Use of lindane has fallen out of favor due to risk for systemic toxicity (eg, seizures, death). Lindane should be used only as an alternative therapy in patients who cannot tolerate other therapies or when other therapies have failed

European and Japanese guidelines recommend against use of this therapy

The treatment regimen for crotamiton is not standardized. The drug can be applied to the entire body from the chin down, reapplied 24 hours later, and washed off 48 hours after the last application. Regimens consisting of application for up to five successive days or longer have also been utilized. In randomized trials, crotamiton has appeared less effective than permethrin.

Malathion 0.05% lotion has been used for scabies based upon case series that suggest efficacy [5]. A single application is typically performed. Malathion is applied to the skin at night and washed off after 8 to 12 hours [1]. Disadvantages of malathion include flammability of the product and relatively high cost.

Crusted scabies — Combination treatment with permethrin and oral ivermectin is considered the preferred first-line treatment for crusted scabies.

Treatment with permethrin alone requires repeated applications, and the failure rate is significant.

●Topical 5% permethrin or topical 5% benzoyl benzoate applied daily for seven days, then twice weekly until cure

AND

●Oral ivermectin (200 mcg/kg/dose) given on days 1, 2, 8, 9, and 15

The use of lindane is contraindicated in patients with crusted scabies due to risk for toxicity.

Endemic scabies — 

Mass drug administration, which involves repeat administration of single doses of therapeutic agents to the entire community, has been shown to be an effective control strategy for scabies in hyperendemic areas.

Oral ivermectin is our preferred intervention given the drug’s efficacy and ease of administration.

Special populations

Children — Given its high efficacy and safetypermethrin is our preferred therapy. However, topical sulfur is typically used for the treatment of infants under the age of two months because of lack of regulatory approval for permethrin use in infants in this age group. 

Lindane should not be given to children under the age of 10 years because of risk for systemic toxicity.

Treatment with oral ivermectin is not recommended for children who weigh less than 15 kg.

Pregnant women — Permethrin is considered safe for use in pregnant and lactating women and is a preferred treatment. Systemic absorption is low, and the drug is metabolized quickly.

Second-line treatments for pregnant women include topical sulfur and benzyl benzoate. Although risk associated with oral ivermectin may be low, data on use in this population are limited.

SYMPTOMS AND COMPLICATIONS

Pruritus — 

Antihistamines may improve pruritus, which may persist for up to four weeks after successful treatment .

Non-sedating antihistamine during the day and a sedating antihistamine at night.

After eradication of mites, medium- or high-potency topical corticosteroids can also be prescribed to control itching. In severe cases, patients can be treated with an oral glucocorticoid taper over one to two weeks, starting with 40 to 60 mg of prednisone daily for adults.

Secondary infection — Pyoderma should be treated with appropriate systemic antibiotics.

Nodules — Nodules from scabies may persist after eradication of mites. Dermoscopy may be helpful for identifying patients with residual active disease

Nodules can be treated with once- to twice-daily application of a potent topical steroid for two to three weeks or intralesional injection of a corticosteroid such as triamcinolone acetonide (5 to 10 mg/mL) 

CONTACTS AND ENVIRONMENT

The onset of symptoms of scabies is often delayed for several weeks; therefore, close personal contacts may have active scabies even in the absence of symptoms.

Community setting 

treat the patient and cohabitants or other individuals who have had prolonged skin-to-skin contact in the preceding six weeks simultaneously because symptoms of scabies may be delayed for up to six weeks in newly infested individuals.

In addition, items used within the preceding several days (clothing, linens, stuffed animals, etc) can be placed in a plastic bag for at least three days or washed with hot water and then ironed or dried in a hot dryer

Rooms used by patients with crusted scabies should be thoroughly cleaned and vacuumed.

Institutional setting — 

Suggested general management measures for asymptomatic individuals who are or have been in contact with a patient with classic scabies include:

●Adherence to appropriate infection control measures when handling patients (eg, avoidance of direct skin-to-skin contact, handwashing)

●Treatment of staff, other patients, and household members who had prolonged skin-to-skin contact with the patient

●Avoidance of skin-to-skin contact with the patient until at least eight hours after treatment

●Laundering of clothing and bedding of the affected patient with a washing machine and dryer utilizing hot water and hot, dry cycles

●Routine cleaning and vacuuming of the room after the patient is discharged from the room

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