Permethrin Application Duration
For scabies, apply permethrin 5% cream to the entire body from head to toe and leave on for 8-14 hours before washing off; for head lice, apply permethrin 1% lotion to damp hair and rinse after 10 minutes.
Scabies Treatment (Permethrin 5% Cream)
The FDA-approved regimen is clear and straightforward 1:
- Apply to entire skin surface from head to soles of feet (approximately 30 grams for average adult)
- Duration: 8-14 hours before washing off (shower or bath)
- Special populations: In infants and geriatric patients, include scalp, temple, and forehead (scabies rarely infests adult scalp but commonly affects these areas in vulnerable populations)
- Retreatment: One application is generally curative; if living mites are demonstrated after 14 days, retreatment is necessary 1
Important Caveats for Scabies
- Persistent pruritus after treatment is not a sign of treatment failure and does not indicate need for retreatment 1
- Recent evidence suggests applying permethrin as a cold cream (stored in refrigerator) for 24 hours on two consecutive days may be more effective than single application (87.2% vs 61.8% cure rate) 2, though this exceeds FDA labeling
- The guideline notes permethrin 5% is "usually applied overnight" for scabies 3
Head Lice Treatment (Permethrin 1% Lotion)
The application protocol differs significantly from scabies 3, 4:
- Pre-treatment: Shampoo hair with non-conditioning shampoo, towel dry
- Application: Apply to damp hair
- Duration: 10 minutes then rinse off
- Retreatment: Repeat in 7-10 days (many experts recommend routine retreatment on day 9) 3
Critical Points for Head Lice
- The 10-minute application leaves a residue designed to kill nymphs emerging from eggs not killed initially 3
- However, modern shampoos with conditioners and silicone-based additives impair permethrin adherence and reduce residual effect 3
- Only 70-80% of eggs are killed with first application, necessitating the second treatment 3, 4
- An alternate schedule of days 0,7, and 13-15 has been proposed for non-ovicidal products 3
Key Differences to Remember
| Indication | Concentration | Duration | Application Site |
|---|---|---|---|
| Scabies | 5% cream | 8-14 hours | Entire body |
| Head Lice | 1% lotion | 10 minutes | Hair only |
Common pitfall: Confusing the two formulations and durations. The scabies cream requires overnight application (8-14 hours), while the lice lotion is rinsed after just 10 minutes. Using the wrong duration significantly impacts efficacy.