How to manage treatment-resistant scabies?

Management of Treatment-Resistant Scabies

For treatment-resistant scabies, a combination of oral ivermectin (200 μg/kg, repeated after 2 weeks) plus permethrin 5% cream is the most effective approach, with 10% sulfur ointment as an alternative when permethrin resistance is suspected. 1, 2

Diagnosis Confirmation

Before proceeding with treatment for resistant cases, confirm the diagnosis:

• Verify presence of mites, eggs, or fecal pellets using microscopy
• Consider epiluminescence microscopy for difficult cases
• Rule out other conditions that may mimic persistent scabies (eczema, contact dermatitis)

Treatment Algorithm for Resistant Cases

First-Line Combination Therapy

1. Oral ivermectin at 200 μg/kg body weight

   • Take with food to increase bioavailability
   • Repeat dose after 2 weeks
   • Contraindicated in children <15 kg and pregnant women 1

2. PLUS Topical permethrin 5% cream

   • Apply from head to toe (including scalp, hairline, neck in infants)
   • Leave on for 8-14 hours before washing off
   • Repeat application after 1 week 1

Alternative Options for Permethrin Resistance

• 10% sulfur ointment - Recent evidence shows superior efficacy compared to permethrin in some populations (treatment success rate significantly higher, p<0.001) 2
• Benzyl benzoate 25% lotion - Effective alternative when permethrin fails 3

Management of Crusted (Norwegian) Scabies

Crusted scabies requires more aggressive treatment:

• Multiple doses of oral ivermectin (typically 3-7 doses on days 1,2,8,9,15,22, and 29)
• Daily application of permethrin or sulfur for 7 days, then twice weekly until cure
• Consider adding keratolytic agents to remove crusts
• Treat secondary bacterial infections with appropriate antibiotics 1

Critical Environmental Management

Environmental decontamination is essential to prevent reinfestation:

• Machine wash and hot dry all clothing, bedding, and towels
• Items that cannot be washed should be removed from body contact for at least 72 hours
• Treat all household members and close contacts simultaneously, even if asymptomatic 1

Follow-Up and Monitoring

• Evaluate after 1 week if symptoms persist
• Retreatment is necessary if:
  • Living mites are demonstrable after 14 days
  • New lesions appear
  • Symptoms persist beyond 2-4 weeks 1

Important Caveats

• Persistent itching for 2-4 weeks after successful treatment is common and not necessarily a sign of treatment failure
• Use topical corticosteroids and oral antihistamines to manage post-scabicidal itch
• Resistance to permethrin is increasingly reported, with unexpected low success rates in some recent studies 2
• Lindane is no longer recommended due to potential neurotoxicity and risk of seizures 1, 4

Special Populations

• Immunocompromised patients: More likely to develop crusted scabies requiring aggressive treatment
• Pregnant women: Permethrin 5% cream is preferred; ivermectin should be avoided
• Infants: Permethrin 5% cream with application to scalp and face; avoid ivermectin in those <15 kg 1

Mass Treatment Considerations

For institutional outbreaks or endemic settings:

• Single dose oral ivermectin (200 μg/kg) can be used for mass treatment
• Repeat dose after 2 weeks
• Coordinate treatment of all residents and staff simultaneously 3, 5