What is the recommended treatment for a patient with a lice infestation?

Recommended Treatment for Lice Infestation

First-Line Treatment

Permethrin 1% cream rinse is the recommended first-line treatment for head lice, applied to damp, towel-dried hair for exactly 10 minutes, then rinsed with warm water, with a mandatory second application 7-10 days later. 1, 2, 3

Application Technique

• Wash hair first with a non-conditioning shampoo (conditioning products prevent proper adherence and cause treatment failure) 1, 3
• Towel dry until damp, not soaking wet 1, 3
• Apply permethrin 1% thoroughly to all hair, paying special attention to the scalp, hairline, neck, temples, and behind ears 1
• Leave on for exactly 10 minutes—not longer or shorter 1, 2
• Rinse over a sink with warm water, not hot water (hot water increases absorption through vasodilation) 4, 1
• Second application on day 7-10 is mandatory because permethrin has only 70-80% ovicidal activity, meaning 20-30% of eggs survive the first treatment 1, 2, 5

Why Permethrin First

• 99% cure rate at 14 days with proper application 6
• Low mammalian toxicity with no allergic reactions in patients with plant allergies 2, 3
• Therapeutically superior to lindane (99% vs 85% cure rate) 6
• Safe for children as young as 2 months 3

Second-Line Treatment (When First-Line Fails)

If live lice are confirmed 7-10 days after a second properly applied permethrin treatment, switch to malathion 0.5% rather than applying permethrin a third time due to likely resistance. 2

Malathion 0.5% Application

• Apply to dry hair (not damp like permethrin) 2, 3
• Allow to air dry naturally—do not use hair dryer 2, 3
• Leave on for 8-12 hours (typically overnight) 4, 2, 5
• Wash off after 8-12 hours 2, 3
• Has the highest ovicidal activity of all treatments, often requiring only a single application 4, 2, 3
• Reapply in 7-9 days only if live lice are still present 2, 3

Critical Safety Warning for Malathion

• Contains 78% isopropyl alcohol, making it highly flammable 4, 3
• Do not use near open flames, sparks, or while smoking 3
• Approved only for children ≥6 months, contraindicated in children <24 months 2
• Risk of severe respiratory depression if accidentally ingested (though no cases reported) 4

Alternative Second-Line Options

Benzyl Alcohol 5%

• Kills lice by asphyxiation, not neurotoxic 4
• Apply for 10 minutes, repeat in 7 days 4
• 75% cure rate at 14 days 4
• Approved for children >6 months 2
• Not ovicidal, so second application is mandatory 4

Spinosad 0.9% Topical Suspension

• Apply to dry hair for 10 minutes 2
• Achieves high cure rates with a single application 2
• Rinse with warm water over a sink 2

Treatments to Avoid

Lindane 1% should NOT be used as first-line treatment and is no longer recommended by the American Academy of Pediatrics. 4, 2, 3

• Risk of severe seizures in children 4, 3
• Low ovicidal activity (30-50% of eggs not killed) 4, 2
• Widespread resistance reported worldwide 4, 2
• Banned in California 4
• FDA warns it should only be used when safer medications fail 4
• Contraindicated in neonates and children <50 kg 4

Critical Management Points

Who to Treat

• Only treat individuals with live lice or nits within 1 cm of the scalp 2, 3
• Examine all household members with a magnifying glass in bright light 5
• Treat family members who share a bed with the infected person 2, 3

Common Pitfalls to Avoid

• Post-treatment itching is NOT treatment failure—it's an inflammatory response that can persist for many days after lice are killed 4, 1, 2, 3
• Do not retreat based on itching alone; only retreat if live lice are seen 7-10 days after treatment 1, 2, 3
• Most "resistance" is actually due to improper application—consider misdiagnosis, noncompliance, or incorrect technique before assuming resistance 2, 3
• Never use conditioning shampoo before permethrin application 1, 3
• Never skip the second application for permethrin 1, 2

Environmental Decontamination

• Wash all clothing, bedding, and linens in hot water [>54°C (130°F)] and dry on hot cycle for at least 20 minutes on the same day as treatment 1, 3, 5
• Soak combs and brushes in hot water [>54°C (130°F)] for at least 10 minutes 5
• Remove items that cannot be washed from body contact for 72 hours (lice cannot survive off the human body for more than 2-3 days) 1, 3
• Vacuum carpets, mattresses, and upholstered furniture 5
• Fumigation of living areas is NOT necessary 1

Nit Removal (Optional but Helpful)

• Use a fine-tooth nit comb after treatment 5
• Apply vinegar or vinegar-based products to hair for 3 minutes before combing to help loosen nits 2
• Nit removal is not necessary to prevent spread but can decrease diagnostic confusion 3

Managing Post-Treatment Symptoms

• Topical corticosteroids and oral antihistamines may relieve post-treatment itching and inflammation 4, 2
• Pruritus, erythema, and ocular irritation are common adverse reactions but not reasons for retreatment 4