What is the recommended treatment for a patient diagnosed with scabies, considering various patient demographics and potential complications?

Scabies Treatment

Permethrin 5% cream applied to all areas of the body from the neck down (and including the scalp in infants and young children) and washed off after 8-14 hours is the first-line treatment for scabies. 1, 2

First-Line Treatment Options

Topical Permethrin (Preferred)

• Permethrin 5% cream is the gold standard topical treatment, offering superior safety and efficacy compared to alternatives 1, 2
• Apply to all body areas from neck down and wash off after 8-14 hours 1, 2
• For infants, young children, and elderly patients, apply scalp-to-toes including the head and face, as these populations commonly have scalp involvement 3
• Repeat application after 7-10 days to address newly hatched mites 4
• Two consecutive daily applications (left on for 24 hours each) show higher cure rates (87.2%) compared to single application (61.8%) 4

Oral Ivermectin (Alternative First-Line)

• Ivermectin 200 μg/kg orally, must be repeated in 2 weeks due to limited ovicidal activity 1, 2
• Take with food to increase bioavailability and epidermal penetration 1, 2
• Particularly useful for institutional outbreaks, patients unable to apply topical treatments properly, and as prophylaxis for close contacts 5
• No dosage adjustment needed for renal impairment, but safety uncertain in severe liver disease 6

Special Populations

Pregnant and Lactating Women

• Permethrin 5% cream is the preferred and safe treatment 1, 7
• Avoid lindane completely due to association with neural tube defects and accumulation in breast milk 6

Children

• Children under 10 years: Use permethrin only; lindane is contraindicated due to neurotoxicity risk 1, 2
• Apply permethrin scalp-to-toes in infants and young children 3

Immunocompromised Patients and Crusted Scabies

• Requires aggressive combination therapy: 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-dose regimens will fail in crusted scabies due to massive mite burden (thousands to millions of mites) 2
• This population is at highest risk for treatment failure and requires closer monitoring 2

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

Lindane 1%

• Apply thinly from neck down, wash off after 8 hours 6
• Use only as last resort due to neurotoxicity risk (seizures, aplastic anemia) 1, 2
• Absolute contraindications: Children <10 years, pregnant/lactating women, extensive dermatitis, immediately after bathing 6, 1, 2
• Resistance reported in some geographic areas 6

Other Alternatives

• Sulfur 6% ointment: Apply nightly for 3 consecutive nights 1
• Crotamiton 10%: Apply nightly for 2 consecutive nights, wash off 24 hours after second application 6, 1
• Benzyl benzoate 25%: 87% cure rate but causes burning sensation in 43% of patients 1

Secondary Bacterial Infection Management

• If impetiginization is present, add fusidic acid 2% cream to permethrin 5%, which significantly improves cure rates (95% vs 35% at day 14) 8
• Staphylococcus aureus is the most common secondary pathogen, followed by Streptococcus pyogenes 8

Contact and Environmental Management

Contact Tracing and Treatment

• Examine and treat ALL sexual, close personal, and household contacts within the preceding month simultaneously, even if asymptomatic 1, 2
• For institutional outbreaks, treat the entire at-risk population 1
• Failure to treat contacts simultaneously is the most common cause of treatment failure 1, 2

Environmental Decontamination

• Machine wash and dry bedding/clothing using hot cycle, or dry clean 1, 2, 7
• Alternatively, remove items from body contact for at least 72 hours 1, 2
• Fumigation of living areas is unnecessary 1, 2
• Keep fingernails closely trimmed to reduce scratching injury 1

Follow-Up and Management of Persistent Symptoms

Expected Post-Treatment Course

• Pruritus may persist for up to 2 weeks after successful treatment due to hypersensitivity reaction to dead mites 1, 2
• This does NOT indicate treatment failure 1, 2

Retreatment Criteria

• Evaluate at 1-2 weeks if symptoms persist 1, 2
• Retreat if: Live mites observed, symptoms persist beyond 2 weeks, or new lesions appear 1, 2
• If first regimen fails, switch to alternative regimen 1, 2

Common Causes of Treatment Failure

• Inadequate application of topical treatment (missing body areas) 1, 2
• Failure to treat all contacts simultaneously 1, 2
• Reinfection from untreated contacts or contaminated fomites 1, 2
• Not repeating ivermectin dose at 2 weeks 1, 2
• Using lindane after bathing (increases absorption and toxicity) 1, 2
• Medication resistance 6

Critical Pitfalls to Avoid

• Never use lindane after bathing or showering - dramatically increases systemic absorption and seizure risk 6, 1, 2
• Never expect immediate symptom resolution - pruritus persisting up to 2 weeks is normal 1, 2
• Never treat the patient alone - simultaneous treatment of all contacts is mandatory 1, 2
• Never use single-application permethrin for crusted scabies - will fail due to massive mite burden 2
• Never skip the second ivermectin dose at 2 weeks - essential due to limited ovicidal activity 1, 2
• Never apply permethrin to eyes - use occlusive ophthalmic ointment for eyelash involvement 7