Ivermectin Dosing for Scabies
The recommended dose of ivermectin for scabies is 200 mcg/kg orally, repeated in 2 weeks (14 days), and must be taken with food. 1, 2
Standard Dosing Protocol
Administer 200 mcg/kg as a single oral dose, then repeat the identical dose exactly 14 days later. 1, 2 For example, a 56-kg patient would receive four 3-mg tablets (12 mg total) per dose. 1
The second dose is mandatory, not optional. 1 Single-dose regimens fail in 42% of cases, while two-dose regimens achieve 98% cure rates. 3 The repeat dose is necessary because ivermectin has limited ovicidal activity and does not kill all life cycle stages of the mite. 4, 5
Always take ivermectin with food. 1, 2 This increases bioavailability and enhances drug penetration into the epidermis where the mites reside. 1
Special Populations and Contraindications
Pediatric Patients
Do not use ivermectin in children weighing <15 kg or children <10 years old. 1, 2 Use permethrin 5% cream instead for this population. 1, 2
Ivermectin may cross the blood-brain barrier and cause neurotoxicity in young children. 6
Pregnancy and Breastfeeding
The CDC classifies ivermectin as "human data suggest low risk" in pregnancy and probably compatible with breastfeeding. 1
Permethrin is particularly recommended for pregnant and lactating women as the safer alternative. 2
Renal and Hepatic Impairment
No dose adjustment required for renal impairment. 1
Use with extreme caution in severe liver disease. 1
Crusted (Norwegian) Scabies
For crusted scabies, use aggressive combination therapy: 2
Oral ivermectin 200 mcg/kg on days 1,2,8,9, and 15 2
PLUS topical 5% permethrin cream applied daily for 7 days, then twice weekly until cure 2
Single-dose regimens will fail in crusted scabies due to the massive mite burden (thousands to millions of mites). 2
Critical Management Steps to Avoid Treatment Failure
Contact Treatment
- Treat all household members, sexual contacts, and close personal contacts within the past month simultaneously, even if asymptomatic. 1, 2 This is the most common cause of apparent treatment failure. 2
Environmental Decontamination
Machine wash and dry all bedding, clothing, and towels using hot cycle, or dry clean, or remove from body contact for at least 72 hours. 2
Fumigation of living areas is unnecessary. 2
Symptom Expectations
Pruritus and rash may persist for up to 2 weeks after successful treatment. 1, 7 This is due to allergic dermatitis from dead mites and does not indicate treatment failure. 1
Do not retreat based on persistent itching alone within the first 2 weeks. 7
Only consider retreatment after 2 weeks if live mites are observed or symptoms persist beyond 2 weeks. 2, 7
Common Pitfalls
Forgetting the second dose is the primary predictor of treatment failure (P < 0.001). 3
Not treating contacts simultaneously leads to reinfection cycles. 1, 2
Retreating too early for persistent itching that is actually post-treatment allergic dermatitis. 1, 7
Using inadequate doses: Some clinicians have tried 400 mcg/kg single doses with good results 8, but the CDC-recommended standard remains 200 mcg/kg repeated in 2 weeks. 1, 2
Alternative Dosing Considerations
While the standard CDC recommendation is 200 mcg/kg repeated in 2 weeks 1, 2, some evidence suggests 400 mcg/kg as a single dose may be effective 8, though this is not the guideline-recommended approach and the two-dose regimen at 200 mcg/kg remains superior in controlled studies. 3