Treatment of Crusted Scabies with Permethrin
Crusted scabies requires aggressive combination therapy with both topical permethrin 5% cream applied daily for 7 days, then twice weekly until cure, PLUS oral ivermectin 200 μg/kg on days 1,2,8,9, and 15. 1, 2
Why Combination Therapy is Essential
Crusted scabies (Norwegian scabies) is fundamentally different from ordinary scabies and cannot be treated with standard single-application regimens. This aggressive infestation occurs in immunodeficient, debilitated, or malnourished persons and is far more contagious than typical scabies. 3 The skin harbors thousands to millions of mites rather than the 10-15 mites seen in ordinary scabies. 4
No controlled therapeutic studies exist for crusted scabies, and substantial treatment failure occurs with single-dose topical scabicide or oral ivermectin alone. 3
Specific Permethrin Application Protocol
Apply permethrin 5% cream to ALL body areas including the scalp, face, neck, and under fingernails - unlike ordinary scabies where neck-down application suffices. 1, 2
Daily application for 7 consecutive days initially, then transition to twice-weekly applications until clinical and microscopic cure is achieved. 1, 2
Leave cream on for 8-14 hours before washing off with each application. 5
Use keratolytic agents (such as 5% salicylic acid) concurrently to remove thick hyperkeratotic crusts, which prevent adequate permethrin penetration. 6
Critical Oral Ivermectin Component
The permethrin regimen MUST be combined with oral ivermectin at specific intervals:
200 μg/kg on days 1,2,8,9, and 15 - this is non-negotiable for crusted scabies. 1, 2
Take with food to increase bioavailability and epidermal penetration. 3, 1
The multiple-dose schedule addresses ivermectin's limited ovicidal activity and the massive mite burden. 3
Common Pitfalls to Avoid
Never use single-application permethrin as recommended for ordinary scabies - this will fail in crusted scabies. 3
Do not skip the oral ivermectin component - topical therapy alone is insufficient given the mite burden and thick crusts. 3, 1
Avoid lindane in this population - crusted scabies patients are often immunocompromised or debilitated, making them vulnerable to lindane neurotoxicity. 3, 1
Treat ALL close contacts simultaneously - crusted scabies is highly contagious and easily spreads to healthcare workers and household members. 7
Environmental and Contact Management
Decontaminate all bedding and clothing by machine washing/drying on hot cycle or removing from body contact for 72 hours. 1, 2
Examine and treat all persons with close contact within the preceding month, including healthcare workers in institutional settings. 1, 2, 7
For institutional outbreaks, treat the entire at-risk population and consult an infectious disease expert. 2
Monitoring and Follow-Up
Pruritus may persist for up to 2 weeks after successful treatment - this is NOT treatment failure. 1, 2
Demonstrable living mites after 14 days indicate retreatment is necessary. 5
Continue twice-weekly permethrin applications until clinical and microscopic cure is confirmed - this may take several weeks. 1, 2
Monitor immunocompromised patients more closely as they have increased risk of treatment failure. 1, 2