Ivermectin Dosing for Scabies
For a typical adult patient with uncomplicated scabies, administer oral ivermectin 200 mcg/kg as a single dose, then repeat the exact same dose in exactly 2 weeks (14 days later). 1, 2
Standard Dosing Protocol
- The CDC-recommended dose is 200 mcg/kg orally, repeated once after 14 days 1, 3, 2
- For practical calculation: a 56-kg patient would receive four 3-mg tablets (12 mg total) as a single dose, then repeat this exact dose 2 weeks later 1
- Always administer ivermectin with food to increase bioavailability and enhance drug penetration into the epidermis 1, 2
Why the Second Dose is Mandatory
- The 2-week repeat dose is non-negotiable because ivermectin has limited ovicidal activity (doesn't kill all eggs), so the second dose targets newly hatched mites 1, 2
- Research supports that a second dose 7-10 days later substantially improves cure rates, confirming ivermectin is not effective against all life cycle stages 4
- Forgetting the second dose is one of the most common treatment failures 1
Special Population Adjustments
Pediatric Patients
- Absolute contraindication in children <10 years old or weighing <15 kg due to potential neurotoxicity from blood-brain barrier penetration 1
- Use permethrin 5% cream instead for this age group 1, 2
Pregnancy and Lactation
- Classified as "human data suggest low risk" and probably compatible with breastfeeding 1
- Permethrin is particularly recommended for pregnant/lactating women as the safer alternative 2
Renal and Hepatic Impairment
- No dose adjustments required for renal impairment 1
- Use with extreme caution in severe liver disease 1
Crusted (Norwegian) Scabies
For immunocompromised patients or those with crusted scabies, use intensive combination therapy: 2
- Oral ivermectin 200 mcg/kg on days 1,2,8,9, and 15 1, 2
- Plus topical permethrin 5% cream applied daily for 7 days, then twice weekly until cure 2
- This aggressive approach is necessary because single-dose therapy fails in crusted scabies due to massive mite burden 2
- Requires specialist consultation 1
Critical Management Steps Beyond Dosing
Contact Treatment
- Treat all household members and sexual contacts within the past month simultaneously, even if asymptomatic 3, 2
- Failure to treat contacts simultaneously is a leading cause of reinfection 2
Environmental Decontamination
- Machine-wash and dry all bedding, clothing, and towels using hot cycle, or dry clean 3, 2
- Alternatively, remove items from body contact for at least 72 hours 2
Common Pitfalls to Avoid
- Expecting immediate symptom resolution: Pruritus and rash may persist for up to 2 weeks after successful treatment due to allergic dermatitis, which does NOT indicate treatment failure 1, 3, 2
- Treat persistent itching with topical corticosteroids and oral antihistamines 1
- Only consider retreatment if live mites are observed or symptoms persist beyond 2 weeks 3, 2
- Taking ivermectin on an empty stomach reduces efficacy 1
- Using ivermectin in immunocompromised patients without specialist consultation, as increased mortality has been reported in elderly, debilitated persons 1
Alternative Dosing Considerations
While some research has explored 400 mcg/kg dosing with single-dose efficacy 5, 6, the CDC-recommended standard remains 200 mcg/kg repeated in 2 weeks 1, 2, which should be followed for typical cases. The higher single dose (400 mcg/kg) showed promise in limited studies but is not the established guideline recommendation 6.