Treatment of Pubic Lice (Phthirus pubis)
First-line treatment for pubic lice is permethrin 1% cream rinse OR pyrethrins with piperonyl butoxide, both applied to affected areas and washed off after 10 minutes. 1
First-Line Treatment Options
Permethrin 1% cream rinse should be applied to all affected areas (pubic hair, trunk, thighs, underarms, and occasionally beard areas), left on for exactly 10 minutes, then rinsed off with warm water 1, 2
Pyrethrins with piperonyl butoxide is an equally effective alternative, applied to dry affected areas for 10 minutes, then thoroughly rinsed 1, 2, 3
Both treatments require a mandatory second application in 7-10 days to kill newly hatched lice from eggs that survived the first treatment 1, 2
These agents have extremely low mammalian toxicity and are available over-the-counter 2, 3
Second-Line Treatment for Resistance or Treatment Failure
Malathion 0.5% lotion is the preferred second-line agent when resistance to permethrin or pyrethrins is suspected or documented 1, 4
Apply malathion to dry affected areas, allow to air dry naturally, then wash off after 8-12 hours 1
Malathion has the highest ovicidal activity (~98%) of all available treatments, often requiring only a single application 1
Critical safety warning: Malathion contains 78% isopropyl alcohol and is highly flammable—no smoking, open flames, or heat-producing devices during treatment 1
Oral ivermectin 250 μg/kg repeated in 2 weeks is an alternative second-line option, though it has limited ovicidal activity and requires the second dose 1, 4
Special Considerations for Eyelash Involvement
Never apply topical pediculicides to the eyes or eyelids 1, 5
For eyelash infestations, manually remove visible lice and nits with tweezers, then apply occlusive ophthalmic ointment or petroleum jelly to eyelid margins twice daily for 10 days to suffocate remaining lice 1, 5
Lindane: Contraindicated in Most Patients
Lindane 1% should NOT be used except as a last resort when all other therapies have failed or cannot be tolerated 1
Lindane carries significant toxicity risks including seizures and aplastic anemia 1
It is absolutely contraindicated in children under 10 years, pregnant/breastfeeding women, persons with extensive dermatitis, and those weighing less than 50 kg 1, 5
Lindane has poor ovicidal activity (only 30-50% of eggs killed) 1
Essential Complementary Measures
Decontaminate all bedding, clothing, and linens by machine washing in hot water [above 54°C/130°F] and drying on the hottest setting for at least 20 minutes on the same day as treatment 1, 2, 3
Items that cannot be washed should be sealed in plastic bags for at least 72 hours or dry-cleaned 2
Evaluate and treat all sexual partners from the preceding 3 months, as pubic lice are sexually transmitted 1, 4
Patients should abstain from sexual contact until both they and their partner(s) complete treatment 1
Understanding Treatment Resistance
Increasing resistance to permethrin and pyrethrins has been documented and is now widespread 1, 6, 7
However, before assuming resistance, consider improper application as the most common cause of treatment failure—ensure the product is applied to completely dry hair, left on for the full duration, and covers all affected areas 1
If live lice are confirmed 7-10 days after a properly applied second treatment, switch to malathion rather than repeating permethrin 1
Common Pitfalls to Avoid
Do not apply permethrin or pyrethrins to wet or damp hair for pubic lice treatment—the affected areas should be dry 2, 3
Post-treatment itching may persist for several days and does not indicate treatment failure unless live lice are visualized 1
Screen for other sexually transmitted infections in all patients with pubic lice, as they are typically sexually acquired 1, 4
Consider sexual abuse in children presenting with pubic lice, as transmission requires close physical contact 5, 7