Crusted Scabies

  • Crusted scabies is a severe form of scabies that occurs most often in patients living in institutions, and in people with compromised cellular immunity, e.g. HIV or those on immunosuppressants.
  • Patients with crusted scabies are often at the heart of an outbreak of classical scabies.
  • Combined oral and topical treatment is favoured for crusted scabies.
  • The European guideline for the management of scabies (2017) recommends treatment of crusted scabies with a combination of topical permethrin 5% cream or benzoate lotion 25% (applied daily for 7 days, then twice weekly until the patient is cured) and oral ivermectin (200 micrograms/kg/dose, with food) as three (days 1, 2,and 8), five (days 1, 2 , 8, 9, and 15), or seven doses (days 1, 2, 8, 9, 15, 22, and 29), depending on the severity of infection.
  • Benzyl benzoate is an irritant and is less effective in scabies than permethrin and malathion. In the UK, it is for use only in adults.
  • For crusted scabies, there is no standard way of describing severity, but a clinical grading scale has been developed and used to guide treatment in a hospital in Australia.

 Classical Scabies

  • In the UK, ivermectin tends to be used for classical scabies only when topical treatments are inappropriate or have been ineffective.
  • No controlled clinical trials have been carried out to establish the most effective dosing regimen for ivermectin in classical scabies.
  • For classical scabies, the European SPC for ivermectin 3mg tablets (Stromectol) recommends a single dose of ivermectin 200 micrograms/kg body weight, with a second dose of ivermectin administered two weeks after the initial dose if the parasitologic examination is positive at this time/new lesions have appeared.
  • Australian guidelines note that ivermectin is not ovicidal and recommend that a second ivermectin dose is given after 8 to 15 days in classical scabies.