皮膚科 劉權毅醫師

Pediculicides
Pediculicides are the most effective treatment for pediculosis capitis (Frankowski, 2004). The ideal pediculicide should be inexpensive, easy to use, highly effective, nontoxic to humans, environmentally friendly, and without potential for development of resistance (Ko & Elston, 2004). In general, pediculicides are not recommended for children younger than 2 years (Frydenberg & Starr, 2003; Roberts, 2002). The use of hair conditioners should be avoided before application of a pediculicide because hair conditioners may coat the hair and protect the lice and nits (Mazurek & Lee, 2000). Many pediculicides are available, with the effectiveness depending on both the individual agent and its formulation. Pediculicides with long residual effect are more likely to be ovicidal. The pediculicide should be applied to the entire scalp. Treatment failures often are the result of noncompliance, improper application of pediculicides, or reinfestation, and, rarely, resistance to pediculicides.

Permethrin
Permethrin is a synthetic pyrethrin that has greater potency and less systemic absorption than its parent compound (Bloomfield, 2002). It does not cause an allergic reaction in patients with plant allergies (Frankowski, Weiner, the Committee on School Health, and the Committee on Infectious Diseases, the AAP, 2002). Permethrin acts via the same mechanism as the natural pyrethrins, by blocking sodium channel repolarization of the head lice neuron with resultant respiratory paralysis and death of the parasite (Jones & English, 2003; Ko & Elston, 2004).

Currently, 1% permethrin (Nix) is the treatment of choice for pediculosis capitis because of efficacy and lack of toxicity (Frankowski et al., 2002; Hansen & O"Haver, 2004). The 1% permethrin cream rinse is applied to the hair and scalp for 10 minutes and then rinsed off. Permethrin is both pediculicidal and ovicidal. It leaves a residue on the hair and remains active for 2 weeks after application (AAP, 2003; Bloomfield, 2002). Nevertheless, most experts advise a second treatment 7 to 10 days later to ensure cure (AAP; Bloomfield).

Pyrethrin-based Products
Pyrethrins are often combined with piperonyl butoxide to provide stability and to potentiate the pediculicidal effects and decrease the development of resistance (Jones & English, 2003). Brand names include RID, R&C, Pronto, A-200, and Clear Lice System. These products are neurotoxic to lice (Frankowski et al., 2002). Percutaneous absorption is minimal, and toxicity in human beings is extremely low (Jones & English). The product should be applied to hair that is first shampooed and then towel dried, left on for 10 minutes, and then rinsed off (Frankowski et al., 2002). Because these agents are not ovicidal, application should be repeated 7 days later (Jones & English). Because natural pyrethrins are extracts from the flowers of chrysanthemums, these products should be avoided in patients allergic to chrysanthemums (AAP, 2003).

Lindane
Lindane or gamma benzene hexachloride (Kwell, Kwellada, Scabene) is an organochloride. It is a gamma-aminobutyric acid inhibitor that kills lice by causing central nervous stimulation and respiratory paralysis (Jones & English, 2003; Ko & Elston, 2004). The product was taken off the US market in 2003. The 1% shampoo is applied to dry hair and left on for 10 minutes, while the 1% lotion is left on overnight before being rinsed off. Because of its low ovicidal activity, repeated application 7 to 10 days later is recommended to eradicate any newly hatched lice (AAP, 2003). The product should be used with caution because of its potential for neurotoxicity and bone marrow suppression (AAP, 2003; Eichenfield & Colon-Fontanez, 1998). It is contraindicated for pregnant or nursing mothers, patients with seizure disorders, and patients with hypersensitivity to the product (AAP; Eichenfield & Colon-Fontanez).

Malathion
Malathion is an organophosphate cholinesterase inhibitor that causes accumulation of acetylcholine at the receptor site, thereby leading to the death of the head lice and ova (Jones & English, 2003). Malathion binds to the sulfur atoms of the hair, which accounts for its residual effect (Jones & English). Malathion is available as a 0.5% lotion. The lotion is applied to dry hair until thoroughly moistened, left to air dry, and then rinsed off after 8 to 12 hours (AAP, 2003; Frankowski et al., 2002). The application should be repeated in 7 to 9 days if live lice are still present at that time (AAP). Because the formulation contains 78% isopropyl alcohol, it is highly flammable and may lead to respiratory depression if ingested (Ko & Elston, 2004; Mazurek & Lee, 2000). In addition, malathion has an unappealing odor. Stinging of skin and eye are other potential complications (Mazurek & Lee). As such, malathion should only be used in cases resistant to other treatment.

Mechanical Removal
Removal of nits after treatment with a pediculicide is usually not necessary (AAP, 2003; Frankowski et al., 2002). Because none of the pediculicides is 100% ovicidal, removal of nits by wet combing (also known as "bug busting") is recommended by some authors (Bloomfield, 2002; Mumcuoglu, 1999). Because wet combing is less effective than a pediculicide, wet combing should not be used as the sole intervention for the treatment of pediculosis capitis in the general population (Roberts, Casey, Morgan, & Petrovic, 2000; Wilson, 1999). Also, wet combing is very labor intensive. Nevertheless, wet combing is the only treatment recommended for children younger than 2 years (Roberts, 2002). Wet combing also should be considered if parents prefer not to use a pediculicide on their child (Roberts).

Other Therapies
Preliminary studies have shown that a combination of 1% permethrin and/or trimethoprim/sulfamethoxazole (trimethoprim 10 mg/kg/day and sulfamethoxazole, 50 mg/kg/day in two divided doses) for 10 days is an effective alternative therapy for pediculosis capitis (Hipolito, Mallorca, Zuniga-Macaraig, Apolinario, & Wheeler-Sherman, 2001). Presumably, trimethoprim/sulfamethoxazole works by destroying the gut flora of the louse, thereby interfering with its ability to synthesize vitamin B. Death ensues from vitamin B deficiency. Such treatment should be reserved for cases not responsive to traditional pediculicides or suspected cases of lice-related resistance to therapy (Hipolito et al.). A recent study suggests that a dry-on, suffocation-based, pediculide lotion (DSP lotion) is effective in the treatment of pediculosis capitis (Pearlman, 2004). Other suffocation agents such as Vaseline, petroleum jelly, oils, and mayonnaise also have been advocated, but most have not been scientifically evaluated.

Environmental Interventions
All household members and close contacts should be examined and treated concurrently if infested (AAP, 2003; Frankowski et al., 2002). Bedmates should be treated prophylactically (AAP). It is advisable to disinfect personal hair care items and bedding (Frankowski et al.). Combs and hair brushes should be treated with pediculicides or soaked in hot water (AAP). Bedding should be laundered in hot water or dry cleaned. Disinfecting furniture is not recommended (Roberts, 2002).

The school or child care facility should be notified so that additional cases can be detected and treated. The "no nits" policies exclude many children from school unnecessarily and are not recommended (AAP, 2003; Ko & Elston, 2004; Nash, 2003). The child should be allowed to return to school or child care facility after proper treatment (Roberts, 2002). The child should be discouraged from close, direct head contact with others (Frankowski et al., 2002).



http://www.medscape.com/viewarticle/517431_5

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