What are the treatment guidelines for treatment-resistant scabies?

Treatment Guidelines for Treatment-Resistant Scabies

For treatment-resistant scabies, a combination of topical permethrin 5% cream applied from scalp-to-toes and oral ivermectin (200 μg/kg) repeated after 14 days is recommended as the most effective approach. 1

First-Line Treatment Failure Assessment

Before proceeding to treatment-resistant protocols, ensure initial treatment was properly administered:

• Verify permethrin 5% cream was applied to the entire body (scalp-to-toes, not just neck down) 1, 2
• Confirm treatment duration was adequate (8-14 hours) 1
• Check if all household members and close contacts were treated simultaneously 1
• Ensure environmental decontamination was performed (washing bedding/clothing in hot water or isolating items for 72 hours) 1

Treatment Protocol for Resistant Scabies

Step 1: Modified Topical Therapy

• Apply permethrin 5% cream from scalp-to-toes (not just neck down as traditionally instructed) 2
• Use cold permethrin cream (refrigerated) applied to entire skin surface for 24 hours 3
• Apply for two consecutive days rather than single application 3
• Repeat the two-day application after 7-10 days 3

Step 2: Combination Therapy

• Add oral ivermectin 200 μg/kg
  • First dose with the initial permethrin application
  • Second dose after 14 days 1, 4
• This combination approach is specifically indicated for otherwise intractable cases 5

Step 3: Environmental Control

• Machine wash all bedding, clothing, and towels in hot water (at least 120°F/49°C) 1
• Items that cannot be washed should be isolated for at least 72 hours 1
• Thorough vacuuming of potentially infested areas 1

Follow-up and Monitoring

• Evaluate patient after 1 week to assess treatment response 1
• Note that pruritus may persist for several weeks after successful treatment and is not necessarily an indication for retreatment 1
• If live mites are still present after 14 days, retreatment is indicated 1
• Consider a second follow-up examination at 4 weeks to verify complete eradication 1

Special Considerations and Pitfalls

Emerging Resistance Concerns

• Recent evidence indicates increasing permethrin resistance in scabies mites, primarily through mutations in voltage-gated sodium channels and enhanced detoxifying enzyme activity 6
• While clinical evidence of widespread ivermectin resistance is lacking, there are anecdotal reports of resistance in crusted scabies cases 6

Common Treatment Failure Causes

1. Improper application of topical agents (not covering all affected areas)
2. Failure to repeat ivermectin treatment
3. Incomplete environmental decontamination
4. Not treating all contacts simultaneously
5. Inadequate patient education about treatment protocols 5

Safety Considerations

• Before treating with ivermectin, exclude Loa loa infection in patients who have traveled to endemic regions 1
• Ivermectin should not be applied to the eyes 1
• While permethrin has low mammalian toxicity, monitor for mild local reactions 1
• Avoid lindane due to potential neurotoxicity 1

By following this comprehensive approach to treatment-resistant scabies, focusing on combination therapy with both topical permethrin (applied correctly from scalp-to-toes) and oral ivermectin, along with proper environmental control measures, most resistant cases can be successfully treated.