Scabies: Types and Treatment Algorithm
Types of Scabies
Scabies presents in two main clinical forms: classical (uncomplicated) scabies and crusted (Norwegian) scabies. 1
- Classical scabies is the typical presentation with burrows, papules, vesicles, and intense nocturnal pruritus affecting finger webs, wrists, axillary folds, abdomen, buttocks, and genitalia 2
- Crusted (Norwegian) scabies is an aggressive infestation occurring in immunodeficient, debilitated, or malnourished persons, harboring thousands to millions of mites and being far more contagious than typical scabies 1
First-Line Treatment for Classical Scabies
Permethrin 5% cream is the gold standard first-line treatment for uncomplicated scabies in otherwise healthy individuals. 1, 3
Permethrin 5% Cream Application Protocol
- Apply to all areas of the body from the neck down and wash off after 8-14 hours 1, 4
- For infants, elderly, and immunocompromised patients, apply scalp-to-toes including hairline, neck, temple, and forehead 1
- Usually 30 grams is sufficient for an average adult 4
- One application is generally curative 5, 4
Oral Ivermectin as Alternative First-Line
- Dosage: 200 μg/kg body weight, with a mandatory second dose after 2 weeks 1, 3
- Must be taken with food to increase bioavailability and epidermal penetration 1, 3
- The second dose is essential because ivermectin has limited ovicidal activity and does not kill eggs present at initial treatment 1
- Not recommended for children weighing less than 15 kg due to potential neurotoxicity 5
Treatment for Special Populations
Pregnant and Lactating Women
Permethrin 5% cream is the preferred treatment for pregnant or lactating women. 1, 5, 3
- Ivermectin is classified as "human data suggest low risk" in pregnancy and probably compatible with breastfeeding, but permethrin remains preferred due to more established safety data 1
Infants and Young Children
- Permethrin is recommended for infants and young children 1, 5
- Application must include scalp, temple, and forehead 1, 4
- Do not use ivermectin in infants less than 2 months old or children weighing less than 15 kg due to potential neurotoxicity 5
- Avoid lindane in children under 10 years due to risk of neurotoxicity 1, 5, 3
Immunocompromised Patients
- Immunocompromised patients are at higher risk for crusted (Norwegian) scabies, requiring more aggressive treatment 1
- Closer monitoring may be necessary as they are at increased risk for treatment failure 3
Subsequent Treatment Options
When Permethrin Fails or Is Unavailable
Recent evidence suggests permethrin may have reduced efficacy, with benzyl benzoate 25% showing superior cure rates. 6
- Benzyl benzoate 25% demonstrated an 87% cure rate compared to 27% for permethrin in a 2024 randomized controlled trial 6
- May cause a burning sensation in 43% of patients 1, 6
- Can be considered when permethrin fails or is unavailable 1
Other Alternative Treatments
- Sulfur 6% ointment: Applied thinly to affected areas nightly for 3 nights, washing off previous applications before reapplying 1
- Crotamiton 10%: Applied nightly for 2 consecutive nights, washed off 24 hours after second application 1, 7
- Lindane 1%: Applied thinly from neck down and washed off after 8 hours, but contraindicated in children <10 years, pregnant/lactating women, and persons with extensive dermatitis due to neurotoxicity risk 1, 5, 3
Treatment for Crusted (Norwegian) Scabies
Crusted scabies requires aggressive combination therapy; single-agent treatment will fail. 1
Combination Therapy Protocol
- 5% permethrin cream applied daily for 7 days, then twice weekly until cure 1, 5
- PLUS oral ivermectin 200 μg/kg on days 1,2,8,9, and 15 1, 5
- The multiple-dose ivermectin schedule addresses the massive mite burden and ivermectin's limited ovicidal activity 3
Critical Management Components
Contact Management
All persons with sexual, close personal, or household contact within the preceding month must be examined and treated simultaneously, even if asymptomatic. 1, 5, 3
- For institutional outbreaks, treat the entire population at risk and consult with an expert 1
Environmental Decontamination
- Machine wash and dry bedding and clothing using hot cycle, dry clean, or remove from body contact for at least 72 hours 1, 3
- Fumigation of living areas is unnecessary 1, 3
- Keep fingernails closely trimmed to reduce injury from scratching 1
Follow-Up and Retreatment Criteria
Expected Post-Treatment Course
Pruritus may persist for up to 2 weeks after successful treatment and is not an indication for retreatment. 1, 3, 4
- Persistent pruritus alone represents a sensitization reaction rather than active infestation 1
When to Retreat
- Consider retreatment if symptoms persist beyond 2 weeks, live mites are observed, or other signs of treatment failure are present 1, 3
- Demonstrable living mites after 14 days indicate that retreatment is necessary 4
- Evaluate patients after 1-2 weeks if symptoms persist 5, 3
Common Treatment Pitfalls to Avoid
Treatment failure most commonly results from application errors and inadequate contact management, not medication resistance. 1
- Failure to treat all close contacts simultaneously 1, 3
- Inadequate application of topical treatments (missing scalp in infants/elderly, not covering all body areas) 1, 3
- Using lindane after bathing or in contraindicated populations (increases absorption and seizure risk) 1, 3
- Not repeating ivermectin dose after 2 weeks 1, 3
- Expecting immediate resolution of symptoms (may take up to 2 weeks) 1, 3
- Incomplete decontamination of furnishings and clothes 8
- Using single-application permethrin for crusted scabies (will fail) 3