What is the recommended treatment for scabies?

Evaluation and Treatment for Scabies

Diagnosis

The diagnosis of scabies is confirmed by identifying burrows, mites, eggs, or fecal pellets on microscopic examination or dermoscopy, but clinical diagnosis based on characteristic findings is often sufficient to initiate treatment. 1, 2

Key diagnostic features include:

• Thread-like papules (burrows) - the pathognomonic finding 3
• Intense nocturnal pruritus - the hallmark symptom 4, 3
• Distribution pattern: finger webs, wrists, axillary folds, abdomen, buttocks, inframammary folds, and male genitalia 4
• Disseminated excoriated erythematous papules on anterior trunk and limbs 5

Diagnostic modalities when clinical suspicion exists:

• Microscopic examination of KOH-prepared skin scrapings 6
• Dermoscopy/epiluminescence microscopy 4, 3
• High-resolution digital photography or biopsy for atypical presentations 6

First-Line Treatment for Uncomplicated Scabies

Permethrin 5% cream is the gold standard first-line treatment for uncomplicated scabies. 1, 2, 6

Permethrin Application Protocol:

• Apply from the neck down to all areas of the body (including under fingernails and to the edge of all body orifices) 1, 2
• Leave on for 8-14 hours, then wash off 1, 2
• Repeat application after 7-10 days (or at day 4 based on mite life cycle for more efficient eradication) 1, 6
• One application is generally curative, though two applications increase efficacy 2, 7
• Store cream in refrigerator and apply cold for better tolerability 7

Oral Ivermectin as Alternative First-Line:

• Dose: 200 μg/kg, repeated in 2 weeks 1, 2
• Must be taken with food to increase bioavailability and epidermal penetration 1, 8
• Contraindicated in children weighing <15 kg due to neurotoxicity risk 2, 8
• No dosage adjustment needed for renal impairment 1

Special Populations

Pregnant and Lactating Women:

Use permethrin exclusively - ivermectin has limited safety data in these populations 2, 8

Infants and Young Children:

• Permethrin is preferred and safe in children ≥2 months old 2, 9
• Do not use ivermectin in children <15 kg 2, 8
• Do not use lindane in children <10 years due to neurotoxicity risk 1, 2
• Safety not established in infants <2 months; avoid ivermectin, lindane, benzyl alcohol, and malathion 2

Immunocompromised Patients:

Require closer monitoring as they are at increased risk for treatment failure 1

Crusted (Norwegian) Scabies

Crusted scabies requires aggressive combination therapy - single-agent treatment will fail. 1, 2

Treatment protocol:

• Topical permethrin 5% cream applied daily for 7 days, then twice weekly until cure 1, 2
• PLUS oral ivermectin 200 μg/kg on days 1,2,8,9, and 15 1, 2
• Take ivermectin with food 1, 8
• Never use single-application permethrin alone - this will fail 1
• Never skip the oral ivermectin component - topical therapy alone is insufficient given the massive mite burden 1

Alternative Treatments (When First-Line Options Unavailable)

• Lindane 1%: Apply for 8 hours, but less effective than permethrin 8, 5
• Benzyl benzoate 25% lotion 5
• Sulfur 6-33% ointment: Apply for 3 consecutive nights 8, 5
• Crotamiton: Apply to entire body, repeat after 24 hours, cleansing bath 48 hours after last application 10, 3
• Malathion 0.5% aqueous lotion 5

Management of Contacts and Environment

All close personal, sexual, and household contacts within the preceding month must be examined and treated simultaneously, even if asymptomatic - this is the most common cause of treatment failure. 1, 2, 8

Environmental Decontamination:

• Machine wash/dry bedding and clothing using hot cycle 1, 2
• Dry clean or remove from body contact for at least 72 hours 1, 8
• Vacuum furniture and carpets 6
• Isolate non-launderables for minimum 2 days (or 3 weeks for rigorous approach) 6
• Fumigation of living areas is unnecessary 1, 8

Follow-Up and Persistent Symptoms

Pruritus and rash may persist for up to 2 weeks after successful treatment - this does NOT indicate treatment failure. 1, 2, 8

• Approximately 75% of patients with pruritus at 2 weeks will have resolution by 4 weeks 9
• Consider retreatment only if symptoms persist beyond 2 weeks AND live mites are observed 1, 2, 8
• Reevaluate after 1-2 weeks if symptoms persist 2

Reasons for persistent symptoms:

• Treatment failure (improper application) 1, 3
• Reinfection from untreated contacts or fomites 1, 3
• Cross-reactivity with other household mites 1

Critical Pitfalls to Avoid

Failure to treat all close contacts simultaneously is the most common cause of treatment failure. 8, 3

Other common errors:

• Inadequate application of topical treatments (missing scalp, face, under nails, body folds) 1, 8, 6
• Not repeating ivermectin dose after 2 weeks 1, 8
• Using lindane after bathing - increases absorption and toxicity risk 1, 8
• Using lindane in contraindicated populations: children <10 years, pregnant/lactating women, extensive dermatitis 1, 2, 8
• Expecting immediate symptom resolution - pruritus can persist 2-4 weeks 1, 9
• Incomplete decontamination of fomites 3
• Lack of written instructions for patients 3

Emerging Concerns

There is a rising number of well-documented cases of poor response to permethrin, though direct proof of resistance has not been established. 3 When standard treatment fails despite proper application and contact management, consider combination therapy with permethrin plus ivermectin. 3