What is the recommended treatment for a patient diagnosed with scabies, considering various patient factors such as immune status and potential for re-infestation?

Scabies Treatment

Permethrin 5% cream applied from the neck down for 8-14 hours is the first-line treatment for uncomplicated scabies, with oral ivermectin 200 μg/kg (repeated in 2 weeks) as an equally effective alternative. 1, 2, 3

First-Line Treatment Options

Topical Permethrin 5% Cream

• Apply to all body areas from the neck down and wash off after 8-14 hours 1, 2, 3
• One application is generally curative in most cases 4
• Preferred for pregnant/lactating women, infants, and young children due to superior safety profile 1, 2, 3
• Safe and effective in children ≥2 months of age 5
• More cost-effective than ivermectin 1

Oral Ivermectin

• Dose: 200 μg/kg body weight, repeated in 2 weeks 1, 2, 3
• Must be taken with food to increase bioavailability and epidermal penetration 1, 2
• The second dose at 2 weeks is essential because ivermectin has limited ovicidal activity 1, 2
• Not recommended for children weighing <15 kg due to potential neurotoxicity 4
• No dosage adjustment needed for renal impairment, but use caution in severe liver disease 1

Special Population Considerations

Pregnant and Lactating Women

• Use permethrin 5% cream exclusively 1, 2, 3
• Avoid ivermectin due to limited safety data in pregnancy 4
• Never use lindane due to association with neural tube defects and mental retardation 1

Infants and Young Children

• Permethrin 5% cream is the treatment of choice 1, 4
• Safe for infants ≥2 months of age 5
• Avoid ivermectin in children <15 kg 4
• Never use lindane in children <10 years due to neurotoxicity risk 1, 2, 3

Immunocompromised Patients

• Higher risk for crusted (Norwegian) scabies requiring more aggressive treatment 3
• Closer monitoring necessary as treatment failure rates are increased 2

Crusted (Norwegian) Scabies Management

This severe form requires aggressive combination therapy, not single-agent treatment. 2, 3

• Topical: Permethrin 5% cream applied daily for 7 days, then twice weekly until cure 2, 3
• Oral: Ivermectin 200 μg/kg on days 1,2,8,9, and 15 2, 3, 4
• Single-application permethrin or single-dose ivermectin will fail due to massive mite burden (thousands to millions of mites) 2
• This population is often debilitated or immunocompromised, making them particularly vulnerable to treatment failure 2

Alternative Treatments (When First-Line Options Fail or Are Unavailable)

Lindane 1%

• Apply thinly from neck down, wash off after 8 hours 1, 3
• Use only if permethrin and ivermectin have failed or cannot be tolerated 1
• Absolute contraindications: children <10 years, pregnant/lactating women, extensive dermatitis, immediately after bathing 1, 2, 3
• Risk of seizures and aplastic anemia, especially with improper use 1
• Resistance reported in some U.S. regions 1

Crotamiton 10%

• Apply nightly for 2 consecutive nights, wash off 24 hours after second application 1, 6
• Less effective than permethrin or ivermectin 1

Sulfur 6% Ointment

• Apply nightly for 3 nights 3
• Alternative when other treatments unavailable 3

Contact and Environmental Management

Contact Tracing and Treatment

• Examine and treat all persons with sexual, close personal, or household contact within the preceding month 1, 2, 3
• Treat all contacts simultaneously, even if asymptomatic, to prevent reinfection 2, 4
• For institutional outbreaks, treat the entire at-risk population 3

Environmental Decontamination

• Machine wash and dry bedding/clothing using hot cycle, or dry clean 1, 2, 3
• Alternatively, remove items from body contact for at least 72 hours 1, 2, 3
• Fumigation of living areas is unnecessary 1, 3
• Keep fingernails closely trimmed to reduce injury from scratching 1, 3

Follow-Up and Expected Course

Normal Post-Treatment Symptoms

• Pruritus, rash, and mild burning may persist for up to 2 weeks after successful treatment 2, 3, 4, 5
• In clinical trials, approximately 75% of patients with persistent pruritus at 2 weeks had resolution by 4 weeks 5
• This does not indicate treatment failure 2, 3

Retreatment Criteria

• Reevaluate at 2 weeks if symptoms persist 2, 3, 4
• Consider retreatment only if live mites are observed or symptoms persist beyond 2 weeks 2, 3, 4
• Some experts recommend retreatment at 1 week for symptomatic patients, though this is not universally agreed upon 1, 2

Reasons for Treatment Failure

• Inadequate application of topical treatments (missing body areas, insufficient contact time) 2, 3
• Failure to treat all close contacts simultaneously 2, 3
• Reinfection from untreated contacts or contaminated fomites 2, 3
• Not repeating ivermectin dose at 2 weeks 2, 3
• Medication resistance (rare but reported with lindane) 1

Critical Treatment Pitfalls to Avoid

1. Never use lindane after bathing - increases absorption and seizure risk 1, 3, 4
2. Never use lindane in contraindicated populations - children <10 years, pregnant/lactating women, extensive dermatitis 1, 2, 3
3. Never skip the second ivermectin dose at 2 weeks - limited ovicidal activity requires repeat dosing 1, 2, 3
4. Never treat crusted scabies with single-agent therapy - requires combination topical and oral treatment 2, 3
5. Never fail to treat all household contacts simultaneously - leads to reinfection 2, 3, 4
6. Never expect immediate symptom resolution - pruritus may persist 2 weeks after successful treatment 2, 3, 4, 5
7. Never apply permethrin to eyes - flush immediately with water if contact occurs 5