What are the directions for using Nix (permethrin) to treat lice?

How to Use Nix (Permethrin 1%) for Head Lice Treatment

To use Nix (permethrin 1%) for head lice, first shampoo with a non-conditioning shampoo, towel dry the hair, then apply the cream rinse for 10 minutes before rinsing off, with a second application recommended 7-10 days later to kill newly hatched lice. 1, 2

Proper Application Technique

1. Confirm diagnosis first:

   • Only treat when live lice are present (not just nits/eggs)
   • The gold standard for diagnosis is finding a live louse on the head 1, 2

2. Preparation:

   • Wash hair with a non-conditioning shampoo
   • Avoid conditioner-containing shampoos as they reduce permethrin's effectiveness 1
   • Thoroughly towel dry the hair (hair should be damp, not wet) 1

3. Application:

   • Apply sufficient Nix 1% permethrin cream rinse to saturate the hair and scalp
   • Pay special attention to the back of the head and neck
   • Leave on for exactly 10 minutes (not less) 1, 2

4. Rinse:

   • Rinse hair thoroughly with warm water (not hot water)
   • Rinse over a sink rather than in shower/bath to limit skin exposure 1
   • Towel dry hair after rinsing

5. Follow-up treatment:

   • A second application is recommended 7-10 days after the first treatment
   • Many experts now recommend routine re-treatment on day 9 1
   • This second application kills newly hatched lice that may have emerged from eggs not killed by the first treatment 1

Important Considerations

• Residual effect: Permethrin leaves a residue on the hair designed to kill nymphs emerging from eggs not killed with the first application 1

• Resistance concerns: Resistance to 1% permethrin has been reported, though the prevalence is not known 1

• Side effects: Possible adverse effects include pruritus (itching), erythema (redness), and edema, which may persist for days after treatment but are not reasons for re-treatment 1

• Treatment failure: If live lice are still present after the second application, consider:

  • Incorrect application technique
  • Reinfestation from untreated contacts
  • True resistance to permethrin 2

• Allergies: Permethrin is less allergenic than pyrethrins and does not cause allergic reactions in individuals with plant allergies 1

Adjunctive Measures

• Combing: While some recommend using a fine-toothed comb to remove nits, research suggests that combing by non-professionals does not significantly improve treatment efficacy 3

• Environmental cleaning:

  • Machine wash clothing, bedding, and hats in hot water
  • Dry on hot cycle for at least 20 minutes
  • Soak combs and brushes in hot water for at least 10 minutes
  • Vacuum furniture and car seats used by affected individuals 2

• Symptom management: For persistent itching after treatment, topical corticosteroids and oral antihistamines may provide relief 1

Nix (permethrin 1%) remains one of the recommended first-line treatments for head lice due to its efficacy and safety profile, though resistance patterns may vary by region 1, 2.