What is the recommended dose of oral ivermectin for the treatment of head lice?

Oral Ivermectin Dosing for Head Lice

For head lice resistant to topical treatments, oral ivermectin should be dosed at 400 μg/kg on day 1 and repeated on day 8, and should only be used in patients weighing at least 15 kg.

Recommended Dosing Regimen

Standard Dose

• Administer 400 μg/kg orally as a single dose, repeated after 7 days 1, 2
• This higher dose (400 μg/kg) has demonstrated superior efficacy compared to the traditional 200 μg/kg regimen 1, 2
• The second dose timing is critical: give on day 8 (7-day interval) to kill newly hatched nymphs 1, 2

Alternative Lower Dose

• A 200 μg/kg dose repeated in 10 days has also been studied, but is less effective than the 400 μg/kg regimen 1, 3, 4
• The 200 μg/kg dose achieved 77.5% cure after single dose, increasing to 92.5% after second dose 3
• In contrast, 400 μg/kg achieved 95.2% cure rates in intention-to-treat analysis 2

Critical Safety Restrictions

Weight and Age Requirements

• Do not use in children weighing less than 15 kg 1, 2
• Ivermectin can cross the blood-brain barrier and block essential neural transmission, with young children at higher risk 1
• This weight restriction is absolute due to neurotoxicity concerns 1, 5

Clinical Context and Indications

When to Use Oral Ivermectin

• Reserve for lice resistant to all topical agents (permethrin, malathion, spinosad, benzyl alcohol) 1, 5
• Consider when topical treatments have failed despite correct application 1, 5
• Particularly useful for difficult-to-treat infestations where resistance is documented 2

Efficacy Evidence

• The 400 μg/kg regimen showed superior efficacy to 0.5% malathion lotion (95.2% vs 85.0% lice-free at day 15) 2
• In per-protocol analysis, 97.1% of ivermectin-treated patients were lice-free compared to 89.8% with malathion 2
• No significant adverse events were reported in comparative trials 2, 3

Important Caveats

FDA Approval Status

• Oral ivermectin is NOT FDA-approved as a pediculicide 1, 5
• This represents off-label use, though supported by clinical evidence 1, 5

Treatment Expectations

• Post-treatment itching may persist for days and does not indicate treatment failure 5
• Topical corticosteroids and oral antihistamines can relieve post-treatment inflammation 1, 5
• All household members should be examined, but only those with live lice or eggs within 1 cm of scalp require treatment 5

Common Pitfall

• Do not assume resistance as the first cause of treatment failure—improper application of topical agents is more common 5
• Ensure topical treatments were applied correctly before escalating to oral ivermectin 5