Ivermectin for Scabies Treatment
For uncomplicated scabies, administer oral ivermectin 200 mcg/kg as two doses separated by 2 weeks, taken with food to enhance bioavailability. 1, 2
Dosing and Administration
Standard Dosing Regimen
- Dose: 200 mcg/kg orally
- Frequency: Two doses, 14 days apart 1
- Administration: Must be taken with food to increase bioavailability and enhance drug penetration into the epidermis 1
The two-dose regimen is critical because ivermectin has limited ovicidal activity and cannot prevent hatching of eggs present at the time of initial treatment 1. Single-dose regimens result in only 58% treatment success compared to 98% with two doses 3, making the second dose essential for treatment success.
Weight-Based Dosing (from FDA Label)
For patients ≥15 kg 2:
- 15-24 kg: 1 tablet (3 mg)
- 25-35 kg: 2 tablets (6 mg)
- 36-50 kg: 3 tablets (9 mg)
- 51-65 kg: 4 tablets (12 mg)
- 66-79 kg: 5 tablets (15 mg)
- ≥80 kg: 200 mcg/kg
Contraindications and Special Populations
Absolute Contraindications
- Infants and children <15 kg: Ivermectin safety is not established in this population 1, 2. Use permethrin 5% cream instead 1
- Severe liver disease: Safety of multiple doses is unknown 1
Relative Contraindications and Cautions
- Elderly, debilitated patients: One study showed increased mortality, though not confirmed in subsequent reports 1. Use with caution and consider permethrin as first-line
- Pregnancy: Classified as "human data suggest low risk" but permethrin is preferred 1
- Lactation: Probably compatible with breastfeeding, but permethrin preferred 1
No Dose Adjustment Required
- Renal impairment: No dosing adjustments needed 1
Special Circumstances
Crusted (Norwegian) Scabies
This aggressive form requires intensive combination therapy 1:
- Oral ivermectin: 200 mcg/kg on days 1,2,8,9, and 15
- Topical permethrin 5% cream: Daily application for 7 days, then twice weekly until cure
- Additional doses: May need ivermectin on days 22 and 29 for severe cases 1
Treatment Failure
If symptoms persist beyond 2 weeks or live mites are observed 1:
- Verify proper application technique
- Consider resistance to medication
- Evaluate for reinfection from untreated contacts
- Retreat with alternative regimen or repeat ivermectin
Critical Management Considerations
Partner and Contact Management
- Look-back period: Treat all sexual and household contacts from the previous 2 months 4
- Avoid contact: Until patients and all contacts complete treatment 1
Environmental Decontamination
- Machine-wash and dry bedding/clothing on hot cycle, or dry clean
- Alternatively, remove from body contact for 72 hours 1
- Fumigation is unnecessary 1
Follow-Up
- Pruritus and rash may persist up to 2 weeks post-treatment (allergic reaction to dead mites) 1
- Symptoms persisting >2 weeks warrant re-evaluation for treatment failure or reinfection 1
- Perform follow-up examination if symptoms persist after 1 week 1
Common Pitfalls to Avoid
- Single-dose treatment: Results in 42% failure rate 3. Always prescribe two doses
- Fasting administration: Significantly reduces bioavailability. Must take with food 1
- Inadequate contact tracing: Failure to treat household/sexual contacts leads to reinfection 1
- Premature retreatment: Post-treatment pruritus is normal for up to 2 weeks and does not indicate failure 1
- Using in children <15 kg: Not approved; use permethrin instead 1, 2
Adverse Events
Most adverse events are mild 5. A new eczematous eruption may occur within 72 hours of treatment in up to 48% of patients 6, which responds to topical corticosteroids and emollients. This represents a hypersensitivity reaction to dying mites, not treatment failure.
HIV and Immunocompromised Patients
HIV-positive patients with uncomplicated scabies receive the same treatment as HIV-negative patients 1. However, immunocompromised patients are at increased risk for crusted scabies and should be managed with the intensive regimen described above 1.