Permethrin for Pediatric Head Lice and Scabies
First-Line Treatment Recommendation
Permethrin 1% cream rinse is the first-line treatment for head lice in children, applied to damp, towel-dried hair for exactly 10 minutes, then rinsed off, with a mandatory second application 7-10 days later. 1, 2
For scabies, permethrin 5% cream is applied from head to toe (including scalp in infants) and left on for 8-14 hours before washing off, with one application generally curative. 3
Head Lice Treatment Protocol
Application Technique for Permethrin 1%
- Apply to damp, towel-dried hair (not soaking wet) after shampooing with non-conditioning shampoo 1, 2
- Leave on for exactly 10 minutes, then rinse with warm water over a sink to limit skin exposure 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
- Low mammalian toxicity and does not cause allergic reactions in patients with plant allergies 1, 2
When Treatment Appears to Fail
Before assuming resistance, consider these common causes of apparent treatment failure: 1, 2
- Improper application technique (most common cause)
- Misdiagnosis (not actually lice)
- Noncompliance with second application
- Reinfestation from untreated household contacts
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. 1 Malathion kills permethrin-resistant lice approximately 10 times faster and has 98% ovicidal activity. 1
Post-Treatment Expectations
- Itching persists for days after successful treatment and is NOT a sign of treatment failure 1, 2
- Topical corticosteroids or oral antihistamines can relieve post-treatment inflammation 4, 2
- Only retreat if live lice are seen 7-10 days after treatment 2
Scabies Treatment Protocol
Application Technique for Permethrin 5%
- Apply from head to soles of feet in all patients 3
- In infants, geriatric patients: include scalp, hairline, neck, temple, and forehead (scabies rarely infests adult scalp but commonly affects these areas in infants) 4, 3
- Leave on for 8-14 hours, then wash off with shower or bath 3
- Usually 30 grams is sufficient for an average adult 3
- One application is generally curative 3
Age Restrictions and Safety
- FDA-approved for infants 2 months and older 3
- Real-world evidence supports safety in infants younger than 2 months: Recent studies demonstrate permethrin 5% is well-tolerated even when applied multiple times in infants under 2 months, with no serious side effects reported 5, 6
- Among dermatologists surveyed, 66.7% prefer permethrin as first-line treatment for infants younger than 2 months, with only 4.3% reporting minor side effects (itching, erythema, xerosis) 5
When to Retreat
- Persistent pruritus after treatment is rarely a sign of treatment failure and is NOT an indication for retreatment 3
- Only retreat if demonstrable living mites are present after 14 days 3
Second-Line Treatment: Malathion 0.5%
Use malathion when permethrin resistance is documented or when first-line treatment fails despite correct application. 1
Application Protocol
- Apply to dry hair, allow to air dry naturally (do not use hair dryer or heat sources) 1, 2
- Leave on for 8-12 hours, then wash off 1, 2
- Has highest ovicidal activity (98%) of all available treatments, often requiring only single application 1
- Reapply in 7-9 days only if live lice are still present 1
Critical Safety Warning
- Contains 78% isopropyl alcohol—highly flammable 2
- Avoid open flames, sparks, cigarettes, and heat sources during application and while hair is drying 2
- FDA-approved for children 6 months and older 1
Third-Line Treatment: Oral Ivermectin
Reserve oral ivermectin for cases resistant to all topical agents (permethrin, malathion, spinosad, benzyl alcohol). 7
Dosing and Safety Restrictions
- Dose: 400 μg/kg as single dose, repeated after 7 days 7
- Absolute contraindication: children weighing less than 15 kg due to risk of crossing blood-brain barrier and blocking neural transmission 4, 7
- Cure rate of 95.2% with 400 μg/kg regimen (superior to older 200 μg/kg regimen) 7
- Not FDA-approved as pediculicide—this is off-label use 4, 7
Treatments to Avoid
Lindane 1% should NOT be used as first-line treatment due to: 1, 2
- Low ovicidal activity (30-50% of eggs not killed) 1
- Seizure risk and neurotoxicity, especially in children 2
- Widespread resistance 1
- Only consider when all other treatments have failed 1
Permethrin 5% is NOT FDA-approved for head lice (only for scabies), though it has been used anecdotally for recalcitrant cases with no proven efficacy advantage over 1% formulation 4
Household and Environmental Management
Who to Treat
- Examine all household members 1
- Only treat those with live lice or eggs within 1 cm of scalp 1, 2
- Treat family members who share a bed with infected person 2
Environmental Decontamination
- Wash all clothing, bedding, linens in hot water and dry on hot cycle on same day as treatment 2
- Wash hair care items (combs, brushes) in hot water 1, 2
- Remove items that cannot be washed from body contact for at least 72 hours (lice cannot survive off human body more than 2-3 days) 2
Nit Removal
- Not necessary to prevent spread, but can decrease diagnostic confusion 2
- Vinegar or vinegar-based products applied for 3 minutes before combing helps loosen nits 1
Common Pitfalls to Avoid
Treating post-treatment itching as treatment failure: Itching commonly persists for days and does NOT indicate need for retreatment unless live lice are present 1, 2
Skipping the second application: Permethrin 1% requires mandatory second application because 20-30% of eggs survive first treatment 1
Applying to wrong hair condition: For head lice, apply to damp (not soaking wet) hair; for malathion, apply to completely dry hair 1, 2
Assuming resistance prematurely: Improper application is the most common cause of treatment failure—verify correct technique before switching agents 1, 2
Using permethrin 5% for head lice: This formulation is not FDA-approved for pediculosis and offers no proven advantage over 1% formulation 4