What are the treatment options for lice infestation?

Treatment of Head Lice (Pediculosis Capitis)

Permethrin 1% lotion is the recommended first-line treatment for head lice, applied to damp hair for 10 minutes, then rinsed, with a mandatory second application in 7-10 days. 1

First-Line Treatment: Permethrin 1%

• Apply permethrin 1% lotion to hair that has been shampooed with a non-conditioning shampoo and towel-dried 2
• Leave on for exactly 10 minutes, then rinse thoroughly 2, 1
• Repeat application in 7-10 days (preferably day 9) to kill newly hatched nymphs from the 20-30% of eggs that survive the first treatment 2, 1
• Permethrin has low mammalian toxicity and does not cause allergic reactions in patients with plant allergies 2, 1

Critical Pitfall to Avoid

Modern shampoos containing conditioners and silicone-based additives impair permethrin's ability to adhere to the hair shaft and reduce its residual killing effect 2. This is why non-conditioning shampoo must be used before application and why routine re-treatment on day 9 is now recommended rather than waiting to see if live lice reappear 2.

Second-Line Treatment: Pyrethrins Plus Piperonyl Butoxide

• Apply to dry hair (not damp like permethrin), leave for 10 minutes, then rinse 2, 3
• Requires second treatment in 7-10 days as 20-30% of eggs remain viable 2
• Avoid in patients allergic to chrysanthemums 2
• Has extremely low mammalian toxicity but resistance has been reported 2

Treatment for Resistant Cases: Malathion 0.5%

Malathion should be used when resistance to permethrin or pyrethrins is documented or when first-line treatments fail despite correct application 2, 1. This is critical because treatment failure is most often due to improper application rather than true resistance 2, 1.

• Apply to dry hair, allow to air dry naturally, then wash off after 8-12 hours 2, 4
• Has high ovicidal activity; single application is usually adequate 2, 1
• Only for patients 24 months of age or older 2, 5
• Highly flammable due to high alcohol content—no smoking, open flames, hair dryers, or electric curlers while hair is wet 2, 4
• Risk of severe respiratory depression if ingested 2, 5

Treatment to Avoid: Lindane 1%

Lindane should not be used as first-line treatment and only considered for patients who cannot tolerate or have failed safer medications 1. Several cases of seizures in children have been reported 2, and it has the highest toxicity profile among pediculicides with central nervous system toxicity being the primary concern 5.

• Low ovicidal activity (30-50% of eggs not killed) 1
• Resistance reported worldwide 2
• Should be left on for no more than 10 minutes 2

Alternative Treatment: Oral Ivermectin

• Single dose of 200 mcg/kg, repeated in 10 days 1
• Should not be used in children weighing less than 15 kg due to risk of crossing the blood-brain barrier 1
• Not FDA-approved as a pediculicide 2, 6

Essential Household Management

All household members must be examined, but only those with live lice or eggs within 1 cm of the scalp should be treated 2, 1, 7. This prevents unnecessary exposure to pediculicides 7.

• Siblings who share a bed with the infested person should be treated even if no live lice are found 7
• Machine wash bedding, hats, scarves, and towels in hot water above 54°C (130°F), then use hottest dryer setting for at least 20 minutes 3
• Soak all combs and brushes in hot water above 54°C for at least 10 minutes 3
• Vacuum carpets, mattresses, and upholstered furniture 3

Nit Removal (Optional but Recommended)

Nit removal after treatment is not necessary to prevent spread but is recommended to decrease diagnostic confusion and for aesthetic reasons 2.

• Use a fine-toothed nit comb on slightly damp hair 3
• Apply vinegar or vinegar-based products to hair for 3 minutes before combing to help loosen nits attached to the hair shaft 2, 1
• Part hair into 1-2 inch sections and comb with firm, even motion away from scalp 3

Adjunctive Symptom Management

• Topical corticosteroids and oral antihistamines may relieve inflammation and itching from the infestation or treatment 2, 1
• Itching or mild burning after treatment is common and not a reason for re-treatment 1

When Treatment Fails: Systematic Approach

Before assuming resistance, consider these causes in order 2, 1, 7:

1. Misdiagnosis (dandruff or hair casts mistaken for nits—confirm by finding live lice) 7
2. Improper application (most common cause) 2, 1, 7
3. Reinfestation from untreated household contacts 2, 7
4. Lack of ovicidal properties requiring second treatment 2
5. True resistance to the pediculicide (prevalence unknown) 2, 1