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 is the first-line treatment for scabies in most patients, applied from the neck down (scalp-to-toes in infants, elderly, and immunocompromised) for 8-14 hours, with oral ivermectin 200 μg/kg (repeated in 2 weeks) as an equally effective alternative, particularly useful for institutional outbreaks or patients unable to apply topical therapy. 1, 2, 3

First-Line Treatment Selection

Standard Scabies (Immunocompetent Adults)

Choose between:

• Permethrin 5% cream: Apply to entire body from neck down, leave on 8-14 hours, then wash off. Single application is generally curative. 1, 2, 3

• Oral ivermectin: 200 μg/kg body weight, taken with food (critical for bioavailability), repeat dose in exactly 2 weeks. 1, 2

Permethrin is preferred over ivermectin because it is more effective, safer, and less expensive for standard scabies, though both are considered first-line options. 2 The second ivermectin dose is non-negotiable—it has limited ovicidal activity and cannot kill eggs present at initial treatment. 2

Special Populations Requiring Modified Approach

Pregnant or lactating women:

• Use permethrin 5% cream exclusively—it is the preferred and safest option. 1, 2, 3
• Ivermectin has limited safety data in pregnancy (classified as "human data suggest low risk") but permethrin remains preferred. 2

Infants and young children:

• Permethrin 5% cream is recommended for children ≥2 months old. 3, 4
• Critical difference: Apply scalp-to-toes including hairline, neck, temple, and forehead—not just neck down. 2
• Avoid ivermectin in children weighing <15 kg due to neurotoxicity risk. 3
• For infants <2 months: Use permethrin only; ivermectin is contraindicated. 3

Elderly and immunocompromised:

• Use permethrin 5% cream with scalp-to-toes application (same as infants). 2
• These patients require closer monitoring as they have increased risk for treatment failure and crusted scabies. 2

Crusted (Norwegian) Scabies

This requires aggressive combination therapy—single-agent treatment will fail. 2

Mandatory 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 (taken with food). 1, 2, 3

The multiple-dose ivermectin schedule addresses the massive mite burden (thousands to millions of mites) and ivermectin's limited ovicidal activity. 2 Single-application permethrin as used for ordinary scabies will fail. 2

Alternative Treatments (When First-Line Options Unavailable or Failed)

Lindane 1%: Apply thinly from neck down, wash off after 8 hours. 5, 1

• Absolute contraindications: Children <10 years, pregnant/lactating women, extensive dermatitis, post-bath application. 5, 1, 2, 3
• Risk of seizures and neurotoxicity, especially with increased absorption after bathing. 5, 2
• Resistance reported in some U.S. regions. 5

Crotamiton 10%: Apply nightly for 2 consecutive nights, wash off 24 hours after second application. 5, 6

Sulfur 6% ointment: Apply nightly for 3 nights, washing off previous applications before reapplying. 1

Environmental and Contact Management (Critical for Preventing Reinfection)

Treat all close contacts simultaneously—this is non-negotiable:

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

Environmental decontamination:

• Machine wash and dry bedding/clothing using hot cycle, or dry-clean, or remove from body contact for ≥72 hours. 5, 1, 2
• Fumigation of living areas is unnecessary. 5, 1, 2
• Keep fingernails closely trimmed to reduce injury from scratching. 1

Follow-Up and Managing Persistent Symptoms

Expected post-treatment course:

• Pruritus may persist for up to 2 weeks after successful treatment—this is normal and represents a sensitization reaction, not treatment failure. 1, 2, 3
• Persistent pruritus alone is NOT an indication for retreatment. 2

When to consider retreatment (after 2 weeks):

• Live mites are observed on examination, OR
• Symptoms persist beyond 2 weeks, OR
• New lesions appear. 1, 2, 3

If retreatment is needed:

• Switch to alternative regimen if first treatment fails. 5
• Reassess for treatment failure causes: inadequate application, untreated contacts, reinfection from fomites, or true resistance. 1

Critical Pitfalls to Avoid

Application errors (most common cause of treatment failure):

• Failing to apply permethrin to scalp/face in infants, elderly, and immunocompromised patients. 2
• Not leaving permethrin on for full 8-14 hours. 1
• Applying lindane after bathing (increases absorption and seizure risk). 5, 2

Contact management failures:

• Not treating all household members and close contacts simultaneously. 1, 2
• Treating patient but not decontaminating bedding/clothing. 1

Medication errors:

• Not repeating ivermectin dose at 2 weeks. 1, 2
• Not taking ivermectin with food (reduces bioavailability). 1, 2
• Using single-agent therapy for crusted scabies. 2

Premature retreatment:

• Retreating for persistent pruritus before 2 weeks when no live mites are present. 2
• Using topical corticosteroids during active treatment phase (may allow mites to proliferate). 2