What is the next step in treating scabies after failure of permethrin (antiparasitic medication) treatment?

Treatment for Scabies After Permethrin Failure

After permethrin treatment failure for scabies, oral ivermectin at a dose of 200 μg/kg, repeated in 2 weeks, is the recommended next step in treatment. 1, 2

Treatment Algorithm After Permethrin Failure

First-Line Alternative Treatment

• Oral ivermectin 200 μg/kg, with a second dose administered 14 days after the first dose 1, 2
• Ivermectin should be taken with food to increase bioavailability and enhance penetration into the epidermis 1, 2
• No dosage adjustments are required for patients with renal impairment, though caution is advised in patients with severe liver disease 1, 2

Factors Contributing to Treatment Failure

• Inadequate application of permethrin (not covering all affected areas) 1
• Failure to treat all close contacts simultaneously 2
• Reinfection from untreated bedding or clothing 1
• Possible resistance to permethrin in some geographic areas 1
• More severe or crusted scabies requiring more aggressive treatment 1

Special Considerations

For Crusted (Norwegian) Scabies

• Combination therapy is recommended: 1, 2
  • 5% topical permethrin 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
  • Additional ivermectin doses on days 22 and 29 may be required for severe cases

For Specific Patient Populations

• Infants and young children: Use permethrin; ivermectin safety not established in children <15 kg 1
• Pregnant or lactating women: Permethrin is preferred, though ivermectin is likely low risk 1, 2
• Immunosuppressed patients (including HIV): At increased risk for crusted scabies and treatment failure; consider consultation with a specialist 1

Environmental Management

• Decontaminate bedding and clothing by machine washing and drying using hot cycle, dry cleaning, or removing from body contact for at least 72 hours 1, 2
• Examine and treat all persons who had close contact with the patient within the preceding month 1, 2
• Fumigation of living areas is unnecessary 1

Follow-Up Considerations

• Rash and pruritus may persist for up to 2 weeks after successful treatment 1
• If symptoms persist beyond 2 weeks or if live mites are observed, retreatment should be considered 1
• Persistent symptoms may be due to: 1, 3
  • Treatment failure
  • Reinfection from untreated contacts or fomites
  • Cross-reactivity with other household mites
  • Allergic dermatitis

Treatment Pitfalls to Avoid

• Using lindane as a second-line agent without proper precautions - it should be avoided due to risks of neurotoxicity, especially in children <10 years, pregnant women, and those with extensive dermatitis 1, 2
• Expecting immediate resolution of symptoms - pruritus can persist for up to 2 weeks after successful treatment 1
• Failing to repeat ivermectin dose after 2 weeks - a second dose is necessary due to ivermectin's limited ovicidal activity 1, 3
• Inadequate environmental decontamination leading to reinfection 2, 3

Evidence on Treatment Efficacy

• Recent evidence suggests that two doses of ivermectin (at a 2-week interval) provides a cure rate of 92.8%, comparable to the efficacy of permethrin 4
• In cases of endemic or difficult-to-treat scabies, ivermectin has shown success where topical treatments including permethrin have failed 5
• For patients with more severe clinical presentation, combination therapy may be more effective than monotherapy 3