Trying to Keep Ahead of Lice: A Therapeutic Challenge

C. E. Malcolm, MD, CCFP; J. N. Bergman MD, FRCPC

Disclosures

Skin Therapy Letter. 2006;11(10):1-6. 

In This Article

Non-neurotoxic Agents

Exoskeleton Integrity Dehydration Pediculicides

A new nonpesticide product containing isopropyl myristate 50% and ST-cyclomethicone 50% (Resultz™, Altana) works by dissolving the waxy exoskeleton of the louse, dehydrating them and eventually leading to their death. The first application is applied to dry hair, the scalp, and the nape of the neck; it is left in place for 10 minutes and then rinsed. A second application, 1 week later is recommended.

Based on safety and efficacy data, Health Canada has recently approved this nonprescription behind the counter product for the treatment of lice in persons aged 4 years and older. Phase II clinical trials document a higher success rate (no live lice) when compared with traditional pediculicides (57% Resultz™ vs. 22% with RID®; 77.1% Resultz™ vs. 20% with permethrin 1%).[17] Other Phase II studies have documented a 97% (28 of 29 patients) success rate.[16] In studies to date, the product was well tolerated with mild local erythema or pruritus being the main side-effect (8 of 29 patients).[16] Phase III clinical trials are pending. Isopropropyl myristate is a water-insoluble organic ester used as an emulsifier and emollient in low concentrations in cosmetic products such as oils, creams, lotions, makeup, lipstick, deodorants, sun screens, hair products, and nail lacquer removers.[18]

Dry-on Suffocation-Based Pediculicide

Nuvo® Lotion, or dry-on suffocation-based pediculicide (DSP) (later found to be Cetaphil® Gentle Skin Cleanser) was reported to have success rate of 96% when applied to the scalp, dried with a hair dryer (for approximately 30 minutes), and removed during the next day´s bath.[12] It was reported to work by suffocating the louses´ spiracles or breathing holes, causing death by suffocation. As reviewed in The Lancet13 and other sources,[14,15] the study did not use proper methods of diagnosing lice, was anecdotal, and was not a well-designed randomized control study. Nevertheless, the concept is novel and there may be a significant beneficial effect; therefore further studies are warranted.

Nit Agents

Further knowledge of the nit sheath, the glue by which the egg is attached to human hair, or the nit laying process may lead to the production of future treatment agents.[19]

Mechanical Removal

Mechanical nit removal as a treatment modality is not an appropriate method of lice eradication when used alone.20 Some authors believe that mechanical removal of nits after treatment with a pediculicide remains an important adjunct.[3] Application of an 8% formic acid rinse or a 1:1 mixture of white vinegar and water followed by combing with a nit comb can aid in the removal of nits. Nit combing is the only treatment recommended for children < 2 years of age. It is labor intensive and somewhat painful.[21]

Environmental Interventions

Clothing, linen and towels should be decontaminated by hot water washing (60ºC) or dry-cleaned. Combs and brushes should be treated with boiling water, alcohol, bleach, or soaked in a disinfectant solution (for example 2% Lysol®).

All household members and close contacts should be examined and treated concurrently if infested; and the school should be notified. Bedmates should be treated prophylactically. Furniture disinfection is unnecessary since head lice generally die within 1--2 days when separated from a person.[5]

Alternative Treatments

Naturopathic products including herbal shampoos, occlusive agents (e.g., mayonnaise, margarine, and olive oil), kerosene or gasoline are largely unproven or ineffective. There is no evidence that the occlusive products suffocate lice and they have no pediculicidal or ovicidal effects.[22] Kerosene or gasoline should never be used due to flammability and extreme hazard. Another "natural" remedy is Chick-Chack®, containing coconut oil, anise oil, and ylang ylang oil.[3] Published data is sparse and caution should be advised until more data is available.

Conclusion

Lice have developed resistance to some pediculicides and it is expected that with ongoing use these pediculicides will probably become less effective. These products can still be used effectively to treat nonresistant lice. Resistance should be suspected if live lice are still present 2--3 days after a product has been used correctly and no other cause for treatment failure can be identified. If lice are present after 2 correctly applied treatments, resistance is almost certain. Resistant infections should be treated with an agent from a different class of pediculicides or with newer non-neurotoxic agents. New products are presently in the process of being developed and tested. Over time these products may prove to be equal to or more effective/safe than the standard neurotoxic pediculicides, while at the same time minimize the problem of treatment resistant lice.

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