How should classic scabies be treated, including first‑line topical permethrin, oral ivermectin for extensive disease or special populations (children, pregnant women, immunocompromised), and management of crusted (Norwegian) scabies?

Treatment of Scabies

First-Line Treatment for Classic Scabies

Permethrin 5% cream is the preferred first-line treatment for classic scabies, applied to all areas of the body from the neck down and washed off after 8-14 hours, with one application generally curative. 1, 2, 3

Application Guidelines by Age Group

• Adults and children ≥10 years: Apply permethrin from the neck down only, avoiding the scalp unless immunocompromised 2, 4
• Infants, young children <2 years, elderly, and immunocompromised patients: Apply permethrin to the entire body including scalp, hairline, neck, temple, and forehead, as these populations commonly have scalp involvement 1, 4, 3
• Approximately 30 grams is sufficient for an average adult 3

Oral Ivermectin as Alternative First-Line

Oral ivermectin 200 μg/kg body weight, repeated in 2 weeks, is an equally effective first-line alternative to permethrin. 1, 2, 5

• Must be taken with food to increase bioavailability and epidermal penetration 1, 5, 4
• The second dose at 2 weeks is essential because ivermectin has limited ovicidal activity and does not kill eggs present at initial treatment 1, 2
• Contraindicated in children weighing <15 kg or younger than 10 years due to potential blood-brain barrier penetration and neurotoxicity 4
• No dosage adjustments required for renal impairment, though safety of multiple doses in severe liver disease is unknown 1

Special Populations

Pregnant and Lactating Women

Permethrin 5% cream is the preferred treatment for pregnant or lactating women. 1, 2, 4

• Ivermectin is classified as "human data suggest low risk" in pregnancy but lacks sufficient safety data 2, 4
• Lindane is absolutely contraindicated due to association with neural tube defects and accumulation in placenta and breast milk 1

Infants and Young Children

Permethrin is the recommended treatment for infants and young children, including those <2 months old. 4, 3

• Lindane should never be used in children <10 years due to high risk of seizures and neurotoxicity 1, 2, 4
• Ivermectin is contraindicated in children weighing <15 kg 4

Immunocompromised Patients

Immunocompromised patients require closer monitoring and are at higher risk for crusted scabies and treatment failure. 2, 5

• These patients should receive scalp-to-toes application of permethrin regardless of age 2

Crusted (Norwegian) Scabies Management

Crusted scabies requires aggressive combination therapy: 5% 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. 1, 2, 5

• Additional ivermectin doses on days 22 and 29 may be required for severe cases 1
• Single-dose topical scabicide or oral ivermectin alone will fail in crusted scabies due to massive mite burden 1, 5
• Crusted scabies occurs in immunodeficient, debilitated, or malnourished persons and is far more contagious than typical scabies 1, 5
• Lindane must be avoided in this population due to risk of neurotoxicity with heavy applications or denuded skin 1, 5
• Specialist consultation is recommended for crusted scabies management 4

Alternative Treatment Options (When First-Line Fails or Unavailable)

Recent evidence suggests declining permethrin efficacy in some regions, making alternatives increasingly relevant:

• Benzyl benzoate 25%: 87% cure rate but causes burning sensation in 43% of patients 2, 6
• Sulfur 6% ointment: Applied nightly for 3 consecutive nights, washing off previous applications before reapplying 2
• Crotamiton 10% cream: Applied nightly for 2 consecutive nights, washed off 24 hours after second application 2
• Lindane 1%: Only if patient cannot tolerate recommended therapies or these have failed; applied thinly from neck down and washed off after 8 hours 1, 2

Lindane Contraindications and Precautions

Lindane should not be used in children <10 years, pregnant/lactating women, persons with extensive dermatitis, or immediately after bathing. 1, 2, 4

• Seizures have occurred when lindane was applied after a bath or used by patients with extensive dermatitis 1
• Aplastic anemia and resistance have been reported 1

Contact and Environmental Management

All persons with sexual, close personal, or household contact within the preceding month must be examined and treated simultaneously, even if asymptomatic. 2, 5, 4

• Bedding and clothing should be machine-washed and machine-dried using hot cycle, dry-cleaned, or removed from body contact for at least 72 hours 1, 2, 4
• Fumigation of living areas is unnecessary 1, 2, 4
• Keep fingernails closely trimmed to reduce injury from scratching 1, 2
• For institutional outbreaks, treat the entire at-risk population concurrently, preferably with mass oral ivermectin for ease of administration 4

Follow-Up and Retreatment Criteria

Pruritus and rash may persist for up to 2 weeks after successful treatment due to allergic dermatitis, not treatment failure. 1, 2, 5

• Persistent pruritus alone is not an indication for retreatment 2
• Retreatment is indicated only after 2 weeks if live mites are observed, symptoms persist beyond 2 weeks, or new lesions continue to appear 2, 5, 4
• Use an alternative regimen if retreatment is necessary 4

Common Reasons for Treatment Failure

• Resistance to medication or faulty application of topical scabicides 1, 5
• Reinfection from untreated contacts or fomites 2, 5
• Failure to treat all close contacts simultaneously 2, 5
• Not repeating ivermectin dose after 2 weeks 2, 5
• Using lindane after bathing or in contraindicated populations 2, 5

Critical Treatment Pitfalls to Avoid

• Do not apply topical corticosteroids during active treatment, as this can suppress inflammatory response and allow mites to proliferate 5
• Do not skip the second ivermectin dose at 2 weeks 2, 5
• Do not use single-application permethrin for crusted scabies—this will fail 5
• Do not expect immediate symptom resolution—allow up to 2 weeks for post-treatment pruritus to resolve 2, 5
• Do not use lindane in children <10 years, pregnant women, after bathing, or in extensive dermatitis 1, 2, 4

Emerging Resistance Concerns

A 2024 double-blinded randomized controlled trial demonstrated only 27% cure rate with permethrin versus 87% with benzyl benzoate, suggesting reduced sensitivity of scabies mites to permethrin in some populations 6. This finding, while concerning, does not yet warrant changing first-line recommendations based on current CDC and FDA guidelines, but clinicians should maintain low threshold for switching to alternative agents if treatment fails 1, 2, 3.