What is the recommended management of scabies, including first‑line topical permethrin 5 % cream for patients ≥2 months old, alternative sulfur ointment for infants <2 months or pregnant/lactating women, and indications for oral ivermectin?

Treatment of Scabies

Permethrin 5% cream applied from the neck down for 8–14 hours (typically overnight) is the first-line treatment for uncomplicated scabies in patients ≥2 months old, with oral ivermectin 200 μg/kg (repeated in 2 weeks) serving as an equally effective alternative or for institutional outbreaks. 1

First-Line Treatment Options

Topical Permethrin 5% Cream

• Apply to all areas of the body from the neck down, leave on for 8–14 hours, then wash off; a single application is generally curative 1
• In infants and young children ≤2 years, apply to the entire body including scalp, hairline, forehead, temples, and neck—not just neck-down as in adults 2
• Permethrin is the preferred agent for pregnant and lactating women due to limited safety data for ivermectin in these populations 3, 1
• For infants <2 months, permethrin remains first-line with 100% complete resolution rates in this age group 4

Oral Ivermectin

• Dose: 200 μg/kg orally, repeated in 2 weeks 1, 5
• Must be taken with food to increase bioavailability and epidermal penetration 1, 5
• Contraindicated in children weighing <15 kg or <10 years old due to potential blood-brain barrier penetration and neurotoxicity 3, 2
• No dosage adjustment needed for renal impairment 5
• Particularly useful when topical application is impractical (e.g., institutional outbreaks, extensive dermatitis) 1, 6

Alternative Topical Agents (when permethrin unavailable or fails)

• Sulfur 6% ointment: Applied nightly for 3 consecutive nights; safest option for infants <2 months 1, 7
• Benzyl benzoate 25%: ~87% cure rate but causes burning sensation in ~43% of patients 2
• Crotamiton 10% cream: Applied nightly for 2 nights, ~60% cure rate versus ~89% for permethrin 2

Special Populations and Clinical Scenarios

Crusted (Norwegian) Scabies

• Requires aggressive combination therapy: 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
• Single-application permethrin or single-dose ivermectin alone will fail due to massive mite burden (thousands to millions of mites) and thick crusts that prevent drug penetration 1
• Mandatory specialist consultation for management 3, 1
• Common in immunocompromised patients (HIV, debilitated, malnourished) who require closer monitoring 3, 1

Pregnant and Lactating Women

• Permethrin 5% cream is the preferred treatment 3, 1
• Ivermectin is classified as "low risk" based on limited human data but permethrin remains first choice 3, 5

Infants <2 Months

• Permethrin 5% cream is recommended; apply to entire body including head and neck 2
• Sulfur 6% ointment is the safest alternative if permethrin is unavailable 1, 7
• Ivermectin is absolutely contraindicated due to neurotoxicity risk 2
• Lindane must never be used 2

Contact and Environmental Management

Simultaneous Treatment of All Contacts

• All household members, sexual partners, and close personal contacts within the preceding month must be treated simultaneously, even if asymptomatic 3, 1
• Scabies has a 4–6 week incubation period during which infected persons remain contagious despite being asymptomatic—untreated contacts are the most common cause of treatment failure 1
• Treating only the symptomatic index case permits asymptomatic household members to reinfect the patient within days to weeks 1

Environmental Decontamination

• Machine-wash and dry all bedding, clothing, and towels on hot cycles, or dry-clean them 3, 1
• Alternatively, remove items from body contact for at least 72 hours (mites cannot survive off-host beyond this period) 1, 2
• Fumigation of living areas is unnecessary 1, 2

Follow-Up and Management of Persistent Symptoms

Expected Post-Treatment Course

• Pruritus and rash may persist for up to 2 weeks after successful treatment due to allergic dermatitis—this does NOT indicate treatment failure 3, 1
• Topical corticosteroids (e.g., triamcinolone) and oral antihistamines can relieve post-treatment pruritus, 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

Retreatment Criteria

• Consider retreatment only after 2 weeks if symptoms persist beyond this period OR live mites are observed 3, 1
• Use an alternative regimen (switch between permethrin and ivermectin) for those who do not respond to initial treatment 3, 1
• Premature retreatment within the first 2 weeks based solely on persistent itching should be avoided 1

Causes of Treatment Failure

• Improper application of topical agents (inadequate coverage, insufficient contact time) 8
• Failure to repeat ivermectin dose after 2 weeks 5, 8
• Reinfection from untreated contacts or contaminated fomites 3
• Incomplete decontamination of bedding and clothing 3, 8
• Absence of written instructions explaining treatment modalities 8

Institutional Outbreaks

• Treat the entire at-risk population simultaneously—control can only be achieved by treating everyone 3, 1
• Mass oral ivermectin administration is recommended for ease of delivery in nursing homes, hospitals, and residential facilities 3, 1, 6
• Manage outbreaks in consultation with a specialist 3, 1

Treatments to Avoid

Lindane

• Never use lindane in children <10 years, pregnant or lactating women, or persons with extensive dermatitis due to risk of neurotoxicity (seizures) and aplastic anemia 3, 1, 2
• Applying lindane after bathing increases systemic absorption and toxicity 1, 2
• Lindane has the highest toxicity profile among scabicidal agents and is strongly discouraged 1

Common Pitfalls to Avoid

• Failure to treat asymptomatic sexual partners and household contacts simultaneously—the most frequent cause of reinfection 1
• Forgetting the second dose of ivermectin at 2 weeks—mandatory due to limited ovicidal activity 5
• Taking ivermectin on an empty stomach—markedly reduces absorption 1, 5
• Expecting immediate resolution of symptoms—post-treatment pruritus is normal for up to 2 weeks 3, 1
• Using single-application permethrin for crusted scabies—will fail due to massive mite burden 1
• Inadequate application of topical permethrin (missing finger webs, genitals, under nails) 8