How do you manage and treat pediculosis (lice infestation)?

Management and Treatment of Head Lice (Pediculosis)

First-line treatment for head lice is permethrin 1% lotion applied to damp, towel-dried hair after shampooing with non-conditioning shampoo, left on for 10 minutes, then rinsed off, with a mandatory second application in 7-10 days. 1

Diagnosis and Initial Assessment

Before initiating any treatment, confirm the diagnosis by finding live lice—nits alone indicate only a historical infestation and do not warrant treatment. 1, 2 Common pitfalls include misdiagnosing dandruff or hair casts as nits, leading to unnecessary pediculicide exposure. 3

Examine all household members: Only treat those with live lice or nits within 1 cm of the scalp. 1 Siblings who share a bed with an infested person should be treated even if no live lice are found. 3

First-Line Pharmacologic Treatment

Permethrin 1% Lotion (Preferred)

• Application technique: Apply to damp hair after shampooing with non-conditioning shampoo (conditioners and silicone-based additives impair permethrin adherence and reduce effectiveness). 1, 3
• Leave on for 10 minutes, then rinse off. 1
• Mandatory second application on day 7-10 to kill newly hatched nymphs, as permethrin has only 70-80% ovicidal activity. 1
• Rinse over a sink with warm water rather than in shower/bath to limit skin exposure. 1
• Use a fine-toothed nit comb after shampooing to remove dead lice and eggs. 4

Permethrin has extremely low mammalian toxicity and does not cause allergic reactions in patients with plant allergies. 1 However, resistance has been reported, though prevalence is unknown. 1, 3

Pyrethrins (Alternative First-Line)

• Apply to dry hair, allow to air dry, then wash off after 8-12 hours (though some evidence suggests 20 minutes may be effective). 5
• Neurotoxic to lice but have extremely low mammalian toxicity. 5

Second-Line Treatment for Resistant Cases

Malathion 0.5% Lotion

Use malathion when resistance to permethrin is documented or when first-line treatments fail despite correct application. 5, 1 Before assuming resistance, consider improper application as the first cause of treatment failure. 1, 3

• Age restriction: Approved for children ≥6 months; contraindicated in children <24 months. 5, 6
• Application: Apply to DRY hair in amount sufficient to thoroughly wet hair and scalp, paying particular attention to the back of head and neck. 4
• Allow hair to dry naturally—do not use hair dryers, curling irons, or flat irons while hair is wet. 5, 4
• Critical safety warning: The product contains 78% isopropyl alcohol and is highly flammable. Do not smoke near a child receiving treatment. 5, 4
• Wash off after 8-12 hours, then shampoo. 5, 4
• High ovicidal activity: A single application is adequate for most patients, but reapply in 7-9 days if live lice are still present. 5, 1, 4
• Toxicity concern: As a cholinesterase inhibitor, there is theoretical risk of respiratory depression if accidentally ingested, though no cases have been reported. 5, 6

Third-Line and Alternative Treatments

Spinosad 0.9% Topical Suspension

• Apply to dry hair and scalp for 10 minutes, then rinse thoroughly with warm water. 1
• Achieves high cure rates with a single 10-minute application. 1

Benzyl Alcohol 5%

• Approved for children >6 months. 5
• Kills lice by asphyxiation (not neurotoxic). 5
• Not ovicidal: Apply for 10 minutes and repeat in 7 days, though consider retreating in 9 days or using 3 treatment cycles (days 0,7, and 13-15). 5
• More than 75% of subjects were free of lice 14 days after initial treatment. 5

Oral Ivermectin

• Single dose of 200 mcg/kg, repeated in 10 days. 1
• Should not be used in children weighing <15 kg due to risk of crossing blood-brain barrier. 1
• Not FDA-approved for pediculosis. 1

Lindane 1% (NOT Recommended)

The American Academy of Pediatrics does not recommend lindane as first-line treatment due to safety concerns. 1, 6 It should only be used for patients who cannot tolerate or whose infestation has failed to respond to safer medications. 1 Lindane has low ovicidal activity (30-50% of eggs not killed), widespread resistance, and seizure risk. 1, 6

Adjunctive Measures

Nit Removal

• Vinegar or vinegar-based products can be applied to hair for 3 minutes before combing to help loosen nits. 1
• Use a fine-toothed nit comb after treatment. 4, 2

Environmental Decontamination

• Wash hair care items and bedding used by the infested person in hot water. 1, 3, 7
• Change pillowcases to prevent reinfestation. 3
• Extensive environmental decontamination is not necessary—spraying or fogging a home with insecticides is not recommended. 7, 8

Managing Post-Treatment Symptoms

• Itching or mild burning of the scalp after treatment is common and not a reason for re-treatment. 1
• Topical corticosteroids and oral antihistamines may help relieve post-treatment inflammation. 1
• Post-treatment itching persists for days and is not treatment failure. 1

Common Pitfalls to Avoid

• Never initiate treatment without clear diagnosis of live lice. 1, 6
• Improper application is the most common cause of treatment failure, not resistance. 1, 3
• Avoid using conditioning shampoos before permethrin application. 3
• Do not treat all family members unnecessarily without evidence of infestation. 3
• "No-nit" policies for schools are not recommended, as nits can persist after successful treatment with no risk of transmission. 2, 7

Special Populations

Pubic Lice

• Treated the same as head lice with permethrin 1% or pyrethrins. 9, 10
• Finding pubic lice should prompt evaluation for other sexually transmitted infections with a look-back period of 3 months. 9, 7, 10

Body Lice

• Suspect in patients with poor hygiene and pruritus who do not change or wash clothing regularly. 5, 9
• Lice may be found in seams of clothing. 5
• Personal hygiene measures and washing affected clothing/bedding are essential—more important than topical treatment. 5, 9