What is the recommended treatment regimen for scabies, including first‑line therapy, dosing, repeat application, alternatives for permethrin intolerance, and precautions for pregnancy, lactation, children, and household contacts?

Scabies Treatment

First-Line Therapy

Permethrin 5% cream is the recommended first-line treatment for uncomplicated scabies in all age groups, including infants, children, pregnant women, and lactating mothers. 1, 2, 3

Application Protocol

• Apply permethrin 5% cream to the entire body from the neck down in adults and older children, leaving on for 8–14 hours (typically overnight), then wash off thoroughly. 1, 3
• Infants and children ≤2 years require application to the entire body including scalp, hairline, forehead, temples, and neck—not just neck-down as in adults. 2
• Approximately 30 grams is sufficient for an average adult. 3
• One application is generally curative. 1, 3

Repeat Application Criteria

• Retreatment is indicated only after 2 weeks if live mites are observed or symptoms persist beyond 2 weeks. 1, 2
• Pruritus and rash commonly persist for up to 2 weeks after successful treatment due to allergic dermatitis—this is not treatment failure and does not warrant immediate retreatment. 1, 2, 3
• If retreatment is needed, consider switching to an alternative agent (e.g., ivermectin). 1

---

Oral Ivermectin as Alternative First-Line

Oral ivermectin 200 μg/kg is an effective alternative to permethrin, particularly when topical application is impractical (e.g., institutional outbreaks, extensive dermatitis, poor adherence). 1, 4

Dosing

• 200 μg/kg orally as a single dose, repeated in exactly 2 weeks. 1, 4
• Must be taken with food to increase bioavailability and epidermal penetration. 1, 4
• For a 56-kg patient, this equals four 3-mg tablets (12 mg total) per dose. 4

Contraindications

• Absolutely contraindicated in children <15 kg or <10 years old due to risk of blood-brain barrier penetration and neurotoxicity. 2, 4
• Not recommended in pregnancy or lactation due to limited safety data; permethrin is preferred. 1, 2, 4
• No dose adjustment needed for renal impairment. 1, 4
• Use with extreme caution in severe hepatic impairment. 4

Common Pitfall

• Forgetting the mandatory second dose at 2 weeks is the most common cause of treatment failure, as ivermectin has limited ovicidal activity. 4

---

Alternative Topical Agents (When Permethrin Unavailable or Fails)

• Sulfur 6% ointment: Apply nightly for 3 consecutive nights (wash off before each reapplication). 1
• Crotamiton 10% cream: Apply nightly for 2 nights, wash off 24 hours after the second application; cure rate ~60% vs. ~89% for permethrin. 2, 5
• Benzyl benzoate 25%: ~87% cure rate but causes burning sensation in ~43% of patients. 2

---

Crusted (Norwegian) Scabies

Crusted scabies requires aggressive combination therapy due to massive mite burden (thousands to millions of mites) and high contagiousness. 1

Recommended Regimen

• 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
• Mandatory specialist consultation for coordination of care. 1, 2

Critical Pitfalls

• Single-application permethrin (as used for ordinary scabies) will fail. 1
• Topical therapy alone is insufficient given the mite burden and thick crusts. 1
• Never use lindane in this population—patients are often immunocompromised or debilitated, making them vulnerable to neurotoxicity. 1

---

Special Populations

Pregnancy and Lactation

• Permethrin 5% cream is the preferred treatment due to limited safety data for ivermectin in these populations. 1, 2
• Ivermectin is classified as "human data suggest low risk" but should be avoided when permethrin is available. 4

Infants <2 Months

• Permethrin 5% cream is safe and effective in infants ≥2 months. 3
• Safety and effectiveness in infants <2 months have not been established. 3
• Ivermectin is absolutely contraindicated in this age group. 2
• Apply permethrin to the entire body including scalp, hairline, and neck. 2

Pediatric Patients

• Permethrin is the treatment of choice for all pediatric patients. 2
• Children ≥10 years (or ≥15 kg) may apply permethrin from the neck down only, unless immunocompromised. 2
• Never use lindane in children <10 years due to high risk of seizures and neurotoxicity. 1, 2

Immunocompromised Patients

• Closer monitoring is necessary as they are at increased risk for treatment failure. 1
• Consider combination therapy (permethrin + ivermectin) even for non-crusted scabies. 1

---

Contact and Environmental Management

All household members, close contacts, and sexual partners within the preceding month must be treated simultaneously, even if asymptomatic, to prevent reinfection. 1, 2

Environmental Decontamination

• Machine-wash and dry all bedding, clothing, and towels using hot cycles, or dry-clean, or isolate from skin contact for ≥72 hours (mites cannot survive off-host beyond this period). 1, 2
• Fumigation of living areas is unnecessary for scabies eradication. 1, 2

Outbreak Management

• During institutional outbreaks, treat the entire at-risk population concurrently. 2
• Mass oral ivermectin is recommended for ease of administration. 2
• Outbreak response should involve specialist consultation. 2

---

Agents to Avoid

Lindane

• Should be avoided entirely due to neurotoxicity (seizures) and aplastic anemia risk. 1, 2
• Absolutely contraindicated in:
  • Children <10 years 1, 2
  • Pregnant or lactating women 1, 2
  • Persons with extensive dermatitis 1, 2
• Never apply lindane after bathing, as this increases systemic absorption and toxicity. 1, 2

---

Post-Treatment Management

Expected Course

• Pruritus and rash may persist for up to 2 weeks after successful treatment due to allergic dermatitis, not active infestation. 1, 2, 3
• Topical corticosteroids (e.g., triamcinolone) and oral antihistamines may relieve symptoms, but only after confirming no live mites are present. 1
• Do not apply corticosteroids during active treatment, as they may suppress the inflammatory response that helps identify active infestation. 1

Evaluation for Treatment Failure

• Reevaluate at 2 weeks post-treatment if symptoms persist. 1, 2
• Retreatment is warranted only if:
  • Live mites are observed after 14 days 1, 3
  • Symptoms persist beyond 2 weeks 1, 2
  • New lesions continue to appear 2
• Switch to an alternative regimen (permethrin ↔ ivermectin) if retreatment is needed. 1

Common Causes of Persistent Symptoms

• Treatment failure (inadequate application, incorrect dosing) 1
• Reinfection from untreated contacts or fomites 1
• Cross-reactivity with other household mites 1

---

Critical Pitfalls to Avoid

• Failure to treat all close contacts simultaneously is the most common cause of reinfection and treatment failure. 1, 2
• Inadequate application of topical treatments (missing body folds, genitals, under fingernails). 1
• Premature retreatment within the first 2 weeks based solely on persistent itching. 1, 2
• Forgetting the second ivermectin dose at 2 weeks. 4
• Using lindane in contraindicated populations. 1, 2
• Not repeating ivermectin dose after 2 weeks. 1
• Expecting immediate resolution of symptoms—allergic dermatitis persists up to 2 weeks. 1, 3