Ivermectin: Proper Use and Dosing for Parasitic Infections
Ivermectin is dosed at 200 mcg/kg orally for most parasitic infections, with a mandatory second dose 14 days later for scabies and pediculosis due to limited ovicidal activity, and must be taken with food to maximize bioavailability and drug penetration into tissues. 1, 2
Standard Dosing by Indication
Scabies
- 200 mcg/kg orally as a single dose, repeated in exactly 14 days 1, 2
- The second dose is mandatory, not optional—ivermectin has limited ovicidal activity and will not kill eggs present at initial treatment 1
- For a 56-kg patient, this equals four 3-mg tablets (12 mg total) per dose 2
Pediculosis Pubis (Pubic Lice)
- 250 mcg/kg orally, repeated in 14 days 1, 2
- Higher dose than scabies due to different parasite biology 1
Strongyloidiasis
- 200 mcg/kg as a single oral dose 3, 4
- Additional doses generally not necessary, but follow-up stool examinations required to verify eradication 3
- Ivermectin achieves significantly higher cure rates than albendazole (RR 1.79,95% CI 1.55-2.08) 4
Onchocerciasis
- 150 mcg/kg as a single oral dose 3
- Retreatment intervals: 12 months for mass campaigns, as short as 3 months for individual patients 3
Crusted (Norwegian) Scabies
- 200 mcg/kg on days 1,2,8,9, and 15 1
- Must be combined with daily topical permethrin 5% or benzyl benzoate 5% for 7 days, then twice weekly 1
- Additional doses on days 22 and 29 may be required for severe cases 1
- This aggressive regimen is necessary because single-dose therapy has substantial failure rates in immunocompromised patients 1
Critical Administration Guidelines
Food Requirements
- Take ivermectin WITH FOOD for scabies, pediculosis, and most parasitic infections to increase bioavailability and enhance drug penetration into the epidermis 1, 2
- Take ivermectin on an EMPTY STOMACH for strongyloidiasis and onchocerciasis per FDA labeling 3
- This distinction is crucial—the food requirement varies by indication 2, 3
Special Population Considerations
Pediatric Patients
- Do not use in children weighing <15 kg—safety has not been established 1, 2
- For children <10 years with scabies, use permethrin instead of ivermectin 1, 2
Pregnancy and Lactation
- Classified as "human data suggest low risk" in pregnancy and probably compatible with breastfeeding 2
Renal Impairment
Hepatic Impairment
- Use with extreme caution in severe liver disease—safety of multiple doses is not established 1, 5, 2
- Patients with severe liver disease may be at higher risk for toxicity 5
Common Pitfalls to Avoid
Forgetting the Second Dose
- The 14-day repeat dose for scabies and pediculosis is mandatory, not optional 1, 2
- Failure to give the second dose will result in treatment failure as eggs hatch after initial treatment 1
Inadequate Contact Treatment
- All household and sexual contacts within the previous month must be treated simultaneously for scabies and pediculosis 1, 2
- Failure to treat contacts leads to reinfection and persistent symptoms 1
Misinterpreting Persistent Symptoms
- Rash and pruritus may persist for up to 2 weeks after successful treatment due to allergic dermatitis 1, 2
- This is NOT treatment failure—do not retreat unless live mites are observed or symptoms persist beyond 2 weeks 1
Environmental Decontamination
- Machine-wash and dry bedding/clothing using hot cycle, or remove from body contact for 72 hours 1
- Fumigation is unnecessary 1
Safety Profile
Adverse Events
- Generally well-tolerated with no significant difference in adverse events compared to albendazole 4
- Significantly fewer adverse events than thiabendazole (RR 0.31,95% CI 0.20-0.50) 4
- Common side effects include dizziness, nausea, and disorientation 4
- High-dose regimens (≥400 mcg/kg) show comparable safety to standard doses, though ocular events may increase in onchocerciasis patients 6
- Adverse reactions decrease significantly with repeated dosing—severe reactions (9%) only occur after first dose 7