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Scabies

Principles of Management of Scabies

Initial therapy

First line: Topical 5% permethrin cream, applied overnight to entire body except face, hair-bearing scalp. Rinse thoroughly and follow decontamination protocol.

  • Treat patient and all household members and close contacts at the same time.
  • For children over 2 months of age: Topical 5% permethrin cream, applied overnight to entire body except areas around the eyes. Rinse thoroughly and follow decontamination protocol. Repeat in one week.
  • For infants under the age of 2 months: Precipitated sulfur 6% in petrolatum to be left on for 24 hours a day for 3 days.
  • Benzyl benzoate (10%) solution is a common alternative in Europe and in Australia; it is applied for 24 hours in most individuals. It may be an alternative treatment for infants < 2 years of age and pregnant women; it is applied for 12 hours in these two patient subsets.
  • For cases of crusted scabies, a combination of topical permethrin and ivermectin is used in children over the age of 5 years of age (>15 kg).
    • Week 1: Topical permethrin, also ivermectin 200 mcg/kg (first dose)
    • Week 2: Topical permethrin
    • Week 3: Topical permethrin, also ivermectin 200 mcg/kg (second dose)
  • Note that single-dose ivermectin is not effective in sterilizing eggs, and a second dose is required at least one week later to eradicate newly hatched mites.
  • Ivermectin should not be given to children under the age of 5 years of age.
  • Decontamination protocol: All clothing and bedding used prior to treatment should be washed in hot water with detergent and dried in a dryer. Non-washable garments, bedding, and other items should be sealed in a plastic bag for 2 weeks or dry-cleaned if possible.
  • Contact precautions: Patients should remain in contact precautions for 24 hours following treatment (e.g., 24 hours after the treatment has been washed off).
  • Patients often need a combination of topical steroids (for the dermatitis; start 24 hours after the anti-parasitic treatment) and systemic antihistamines (for itch).
    • For patients with dermatitis, prescribe a medium-potency topical steroid (such as triamcinolone acetonide 0.1% lotion, cream, or ointment applied b.i.d.).
    • For patients with pruritus, prescribe oral antihistamines.
  • All effective anti-pruritic agents can result in drowsiness as a side effect.
    • Start by prescribing an evening dose, taken approximately 1 hour prior to bedtime. Give oral antihistamines (hydroxyzine, such as Atarax or Vistaril)
    • Hydroxyzine suspension (10 mg/5 cc)
    • Doxepin suspension (10 mg/cc)
    • Diphenhydramine (such as Benadryl, 5 mg/kg/day maximum) may be substituted for hydroxyzine as it has less-sedating effect.
    • Loratadine (Claritin┬«) and cetirizine hydrochloride (Zyrtec┬«) suspension can be also used.
  • If the diagnosis of scabies is not confirmed by skin scraping, yet the clinical findings are highly suspicious, it is reasonable to treat with a single application of permethrin 5% cream.
  • Persons who have thick or crusted lesions frequently require a repeat course of treatment, or require a keratolytic agent (such as topical urea or salicylic acid cream) as an adjunctive treatment.

Pitfalls

  • Most therapeutic failures are related to improper use of the topical agents. The topical scabicides must be applied to the whole cutaneous surface (below the neck, except in young children and those with head and neck lesions). Antiscabetic medications are never applied to the lesions only. Care must be taken to apply the topicals carefully between the fingers and toes and under the fingernails, which should be trimmed short. If hands are washed during the treatment period, the medication must be reapplied.
  • Another major reason treatment fails is that all affected persons are not treated at the same time. All family members, even if they do not itch, must be treated. In households where there are babies, this includes babysitters and occasional visitors who have held the baby. Infested persons may not itch for 4-6 weeks after acquiring infection, yet may infect others.
  • Patients often report persistent pruritus despite adequate treatment for scabies. This may be due to persistence of inflammatory cells or mediators in the areas of previously affected skin. It is important to evaluate patients with this common complaint to determine whether they have new lesions suggestive of persistent infestation. Pruritus should be managed with combination therapy of topical corticosteroids (started 24 hours after the initial treatment), gentle skin care, and systemic antihistamines.
  • Bacterial superinfection with Staphylococcus aureus infection is very common. The presence or development of pustules, folliculitis, or cellulitis should be evaluated with high suspicion of bacterial superinfection. A bacterial culture should be performed. For those with secondary infection, give oral antistaphylococcal antibiotics for 1 week.
  • Lesions of scabies may develop into non-infectious prurigo nodules. Involvement of the genitalia is common and may require intralesional corticosteroid treatment.

When to refer to a dermatologist

  • If the diagnosis of scabies is not clear.
  • If the skin eruptions persists despite repeated treatments.
  • For management of nodular scabies or lesions requiring intralesional corticosteroids.