What are the recommended prescription treatments for lice infestation?

Prescription Lice Treatment

For prescription treatment of head lice, start with malathion 0.5% lotion applied to dry hair for 8-12 hours, repeated in 7-9 days if needed, or consider newer agents like spinosad 0.9% or topical ivermectin 0.5% for resistant cases. 1

First-Line Prescription Options

Malathion 0.5% Lotion

• Apply to DRY hair in sufficient amount to thoroughly wet hair and scalp, paying particular attention to the back of the head and neck 1
• Leave on for 8-12 hours, then shampoo and use fine-toothed comb to remove dead lice and eggs 1
• Repeat application after 7-9 days if live lice remain present 1
• Critical safety warning: Malathion is flammable—avoid open flames, electric heat sources, hair dryers, and smoking while lotion is on hair or hair is wet 1
• Allow hair to dry naturally and remain uncovered 1

Spinosad 0.9% Topical Suspension

• Superior efficacy compared to permethrin: 84.6-86.7% of patients lice-free at 14 days versus 42.9-44.9% with permethrin (P < 0.001) 2, 3
• Effective against permethrin-resistant lice 3
• Both pediculicidal and ovicidal activity 3
• Well-tolerated with minimal adverse effects 2, 3
• Approved for children 4 years and older 3

Topical Ivermectin 0.5% Lotion

• Single application treatment: 73.8% lice-free at day 15 versus 17.6% with vehicle control (P < 0.001) 4
• Requires only one application—kills lice by causing pharyngeal muscle paralysis, preventing feeding even after eggs hatch 4
• Minimal systemic absorption 4
• Most common adverse effect: pruritus (0.9%) 4
• Should be reserved as third-line treatment due to limited clinical experience and cost 4

For Difficult-to-Treat or Resistant Cases

Oral Ivermectin

• Oral ivermectin 400 mcg/kg on days 1 and 8 showed superior efficacy to malathion 0.5%: 95.2% lice-free versus 85.0% (P < 0.001) 5
• Contraindicated in children weighing less than 15 kg due to risk of crossing blood-brain barrier and causing neurological adverse effects 6
• Not FDA-approved as a pediculicide 6
• Consider for refractory cases in appropriate weight patients 5

Permethrin 5% Cream

• Available by prescription for recalcitrant cases 6
• Evidence suggests lice resistant to 1% permethrin will not respond to higher concentrations 6
• Not FDA-approved as a pediculicide 6
• Limited efficacy data from randomized controlled trials 6

Agents NOT Recommended

Lindane

• No longer recommended by the American Academy of Pediatrics 6
• Contraindicated in neonates, children weighing less than 50 kg, those with HIV, and patients on medications lowering seizure threshold 6
• Banned in California 6

Sulfamethoxazole-Trimethoprim

• Not FDA-approved as pediculicide 6
• Risk of severe allergic reactions including Stevens-Johnson syndrome makes it undesirable when alternatives exist 6

Important Management Principles

Application Technique

• Rinse all topical pediculicides over a sink (not shower/bath) with warm (not hot) water to minimize skin exposure and absorption 6, 7

Post-Treatment Symptoms

• Itching or mild scalp burning from inflammation can persist for many days after lice are killed and is NOT a reason for re-treatment 6, 7
• Consider topical corticosteroids or oral antihistamines for symptomatic relief 6, 7

Household Management

• Evaluate all family members for infestation and treat if infested 1

Clinical Algorithm for Selection

1. Initial treatment: Malathion 0.5% (if flammability precautions acceptable) or spinosad 0.9% 1, 2, 3
2. If resistance suspected or treatment failure: Spinosad 0.9% or topical ivermectin 0.5% 2, 4, 3
3. For truly refractory cases in patients ≥15 kg: Consider oral ivermectin 400 mcg/kg 5
4. Avoid: Lindane, sulfamethoxazole-trimethoprim, permethrin 5% 6