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V o l u m e 1 1 • N u m b e r 1 0 • D e c e m b e r 2 0 0 6 - J a n u a r y 2 0 0 7 I n d e x e d b y t h e U S N a t i o n a l L i b r a r y o f M e d i c i n e a n d P u b M e d EDITOR-IN-CHIEFStuart Maddin, MDUniversity of British Columbia, Vancouver, Canada Trying To Keep Ahead of Lice:
ASSOCIATE EDITORSHugo Degreef, MD, PhD - Medical DermatologyCatholic University, Leuven, Belgium A Therapeutic Challenge
Jason Rivers, MD - Medical DermatologyUniversity of British Columbia, Vancouver, Canada Jeffrey S. Dover, MD - Surgical Dermatology C. E. Malcolm, MD, CCFP1 and J. N. Bergman MD, FRCPC2 Yale University School of Medicine, New Haven, USADartmouth Medical School, Hanover, USA 1 University of British Columbia Student Health Services, Vancouver, Canada 2 Department of Dermatology and Skin Science, University of British Columbia, and The Pediatric Allergy Dermatology Centre (PADC), Vancouver, Canada Northwestern University Medical School, Chicago, USA Kenneth A. Arndt, MDBeth Israel Hospital Pediculosis capitis, or head lice, is a world-wide public health concern affecting persons of all ages and socioeconomic backgrounds. It is caused by Pediculus Wilma Fowler Bergfeld, MDCleveland Clinic, Cleveland, USA humanus capitis, an obligate ectoparasite that lives on human hair and feeds on the blood from the skin. Upon diagnosis, treatment should be initiated, University of Amsterdam, Amsterdam, Holland since established infestations with head lice generally do not spontaneously University of British Columbia, Vancouver, Canada resolve. Chemical pediculicides are currently the standard treatment, however, Bryce Cowan, MD, PhD University of British Columbia, Vancouver, Canada issues of resistance have made it necessary to explore new alternatives. If an infestation is resistant to these drugs, then the physician should consider treating with an agent from a different class of pediculicides or, potentially, with newer Boston University School of Medicine, Boston, USA Christopher E.M. Griffiths, MDUniversity of Manchester, Manchester, UK Key Words: pediculosis capitis, head lice, pediculicide
Aditya K. Gupta, MD, PhD, MBA/MCMUniversity of Toronto, Toronto, Canada In the US, the number of head lice infestations annually is estimated between Mark Lebwohl, MDMt. Sinai Medical Center, New York, USA 6–12 million among children 3–12 years of age.1 The social, economic and James J. Leydon, MDUniversity of Pennsylvania, Philadelphia, USA educational impact of head lice infestations is considerable. In the US, the total direct costs for treatment and indirect costs for lost wages, educational University of British Columbia, Vancouver, Canada programs, and school and nursing home monitoring programs have been Howard I. Maibach, MDUniversity of California Hospital, San Francisco, USA estimated at more than $1 billion annually.2 Jose Mascaro, MD, MS University of Barcelona, Barcelona, Spain Infestation is most common in school-aged children with girls being more Larry E. Millikan, MDTulane University Medical Center, New Orleans, USA commonly affected than boys. African-American children are less often affected; this variation is thought to be the result of differences in the hair Centre Hospitalier Universitaire de Nice, Nice, France shaft structure, which may be oval shaped and thus more difficult for a louse Ted Rosen, MDBaylor College of Medicine, Houston, USA to grasp.1 Transmission of head lice most commonly occurs through close Alan R. Shalita, MDSUNY Health Sciences Center, Brooklyn, USA physical contact, especially head-to-head contact, but fomites, such as hats also play a role. Louse transfer has been found to be optimal when hairs are relatively stationary and parallel, suggesting that louse transmission is more University of British Columbia, Vancouver, Canada likely to occur while children are at rest, than during periods of vigorous Stephen K. Tyring, MD, PhD, MBAUniversity of Texas Health Science Center, Houston, USA John Voorhees, MDUniversity of Michigan, Ann Arbor, USA Head lice infestation is caused by the obligate ectoparasite Pediculus humanus capitis, a wingless, elongated, dorsoventrally flattened insect. The adult louse Jefferson Medical College, Philadelphia, USA feeds 4–5 times/day and can normally only survive for 1–2 days away from the scalp. Eggs are glued to the hair in egg castings, or nits, close to the scalp and can survive up to 10 days away from the human host. Lice typically lay nits within 1–2mm of the scalp and for practical purposes, nits within 1cm of the scalp should be counted as a sign of active infestation.4 a result of reinfestation from an untreated classmate, Although some children with infestation are inadequate quantity of pediculicide applied, or improper asymptomatic, the most common symptom is pruritus, duration of product application.4 A recent paper which occurs due to sensitization to either louse salivary suggested that a second treatment of the prescribed or fecal antigens and may be so intense that excoriations standard pediculicides (except permethrin) should be and secondary bacterial infection may occur.5 administered ideally 10 days after the start of treatment Many children with an active infestation will, on exam, to kill all active stages of the louse.9 However, in have nits attached to their hair and some live lice on practice many physicians retreat in 7 days instead of their scalp. The diagnostic gold standard for head lice 10. Resistance should be suspected after the second is finding a live louse or nymph on the scalp or a viable treatment if live lice are still present 2-3 days after a egg attached to the hair.5 Nits alone are not proof of product has been used correctly and no other cause active infection because some of these represent hatched for failure can be identified.1 If lice are present after empty shell casings or nonviable eggs that may retain 2 correctly applied treatments, resistance is certain.1 a viable appearance for weeks after death. Microscopic Resistant infestations should be treated with an agent examination of the nit, or use of a hand lens, may aid in from a different class of pediculicides or with newer this determination.4 Since lice move rapidly, not finding a louse does not completely rule out infestation. The use Since permethrin resistance may be a relative of louse combs increases the diagnostic yield.3 If head lice phenomenon, some clinicians will use higher is diagnosed, then it should be treated, since established concentrations and longer durations of contact in an infestations, in general, do not spontaneously resolve. attempt to overcome this resistance. Whether increasing the permethrin concentration from 1% to 5% and leaving it on overnight affects the cure rate is unclear. The ideal treatment agent for lice would be free Certainly this pattern of treatment may cause a higher of harmful chemicals, readily available without a rate of skin irritation, but longer contact with the same prescription, easy to use, and inexpensive.5 Chemical products is already used with other ectoparasites, such pediculicides are currently the standard treatment.
Prior to the emergence of resistance, the treatment of ‘No nit’ policies exclude children from school choice in North America was permethrin 1% due to unnecessarily and are not recommended.4 The presence its safety and efficacy. Unfortunately resistance to of nits alone should not be the basis for exclusion of permethrin and lindane is common in populations where children from school. The child should be allowed to these pediculicides have been heavily used.3 To illustrate return to school or child care facilities after proper this, the insecticidal activity of pyrethroids in the mid 1980s was 100%, but by 2000 it had decreased to only 28%.6 Conversely Meinking, et al., in a recent study, showed 1% lindane was the slowest and least effective Myths about head lice are abundant and belief in these pediculicide with no lice eradicated after 10 minutes myths is often why treatments are not used properly and (the recommended application time), and killing only why people believe their lice treatment has failed. (See 17% of lice after 3 hours.7 Malathion (Ovide®, Taro Pharmaceuticals), which had not been used extensively in the US, has performed well in permethrin-resistant Standard Pediculicides: Neurotoxic Agents populations.3 Lice resistance to both pyrethrin and These agents are historically considered the standard malathion has been documented in the UK (Downs, et al. treatment and have been the most effective treatment showed a 64% failure rate for malathion).8 The pattern for head lice. This category of pediculicides is not of resistance in an area generally follows the pattern recommended for children under 2 years of age and off- of pediculicide use, and this geographic variation in label use of these products for patients in this age range sensitivities further reinforces the belief that lice adapt to toxins and develop resistance with ongoing exposure. These products should be applied to the entire scalp. Because hair conditioner may coat the hair and protect While treatment failures may be due to drug resistance, the lice and nits, it should be avoided before product it is important to recognize many treatment failures are Skin Therapy Letter • Editor: Dr. Stuart Maddin • Vol. 11 No. 10 • December 2006 - January 2007 All children with lice scratch or itch.
Initial infestation may produce no signs or symptoms for 4–6 weeks.
Lice can be dislodged from hair by air movements giving the appearance of flying.
Lice live in carpets, beds, clothes, and sofas Lice can only live for 24-48 hours away from a human host.
Lice die immediately after treatment.
Lice may take several hours to die following treatment.
Due to loss of residual activity of pediculicides, two treatments are recommended to kill newly hatched nymphs.
Permethrin based products are 100% ovicidal.
Permethrin kills 70% of eggs with one treatment.
Everyone in the family should be treated.
Only those with a proven infestation should be treated, although everyone should be checked daily to weekly.
Head lice prefer long or dirty hair.
The likelihood of infestation is not affected by hair length or cleanliness.
Table 1: Myths and facts about head lice10
Permethrin
should be used with caution, as its base is flammable Permethrin 1% (Nix®) is a poorly absorbed synthetic and may lead to respiratory depression if ingested pyrethrin with pediculicidal and ovicidal activity. It (although there are no reported cases).4 Currently blocks sodium channel repolarization of the louse significant resistance to this agent has not been reported neuron resulting in respiratory paralysis and death. in the US, but may occur with ongoing use as seen in By leaving a residue on the hair, it remains active for 2 weeks following application.5 After washing hair, rinsing with water, and towel drying, it is applied to the scalp and hair for 10 minutes and then rinsed out. Lindane (gamma benzene hexachloride) 1% lotion is To ensure a cure, many practitioners recommend a pediculicidal but it has limited ovicidal activity. This second treatment approximately 1 week later as any organochloride kills lice by causing CNS stimulation eggs not killed by first treatment will be hatching.
and respiratory paralysis. Given lindane’s increased side-effect potential including neurotoxicity and Permethrin-based Products
bone marrow suppression, it is considered a second- line treatment.5 Lindane remains on the market as an counter (OTC) extracts of natural pyrethrins from alternative when other treatments have failed. It is chrysanthemums combined with piperonyl butoxide contraindicated in children under 2 years, pregnant to increase stability and effect. These products are neurotoxic to lice but not ovicidal and even after two treatments viable lice and eggs may remain. These products are contraindicated in patients who Ivermectin
are allergic to ragweed, chrysanthemums, or other Ivermectin, an antihelminthic drug, has been suggested for off-label use in the treatment of head lice at a dosage of 200μg/kg, repeated in 7-10 days to kill newly Malathion
hatched nymphs.11 It is an effective pediculicide and the Malathion is an organophosphate cholinesterase mechanism of action is thought to be on the symbiotic inhibitor that causes respiratory paralysis of the louse. gram-negative bacteria that are required to digest blood. It is a fast acting pediculicide that presently has the With the concern of possible neurotoxicity, the safety highest ovicidal activity. It binds to the sulfur atoms of and efficacy of this agent for head lice remains to be the hair, accounting for its residual effect. Malathion established.3 No resistance has been reported to date and 0.5% can be applied for 10 minutes or overnight and it may be used after failure with topical pediculicides. repeated in 1 week. It has an unappealing odor and Treatment with this agent may benefit patients with can cause stinging of the skin and eyes.5 This product extensive infestations or infestations with multiple types Skin Therapy Letter • Editor: Dr. Stuart Maddin • Vol. 11 No. 10 • December 2006 - January 2007 of ectoparasites.3 Oral ivermectin should not be used in their death. The first application is applied to dry hair, children weighing less than 15kg.4 Topical ivermectin the scalp, and the nape of the neck; it is left in place for holds some promise but warrants further study.3 10 minutes and then rinsed. A second application, 1 week later is recommended.
Based on safety and efficacy data, Health Canada has Oral TMP/SMX has been shown to be effective in recently approved this nonprescription behind the small studies of off-label use.5 It presumably works by counter product for the treatment of lice in persons destroying the gut flora of the louse, thereby interfering aged 4 years and older. Phase II clinical trials document with its ability to synthesize vitamin B and ultimately a higher success rate (no live lice) when compared causing death.5 Combination therapy with topical agents 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 Exoskeleton Integrity Dehydration Pediculicides
product was well tolerated with mild local erythema or A new nonpesticide product containing isopropyl pruritus being the main side-effect (8 of 29 patients).16 myristate 50% and ST-cyclomethicone 50% (Resultz™, Phase III clinical trials are pending. Isopropropyl Altana) works by dissolving the waxy exoskeleton of myristate is a water-insoluble organic ester used as the louse, dehydrating them and eventually leading to an emulsifier and emollient in low concentrations in Treatment
Available Brand
Comments
Categories
treatment; however instance of resistance have made it necessary to explore new Permethrin-based • Not recommended for children <2 yrs • Dry-on suffocation-based pediculicide Table 2: Treatment categories for lice therapies
Skin Therapy Letter • Editor: Dr. Stuart Maddin • Vol. 11 No. 10 • December 2006 - January 2007 cosmetic products such as oils, creams, lotions, makeup, ineffective.22 There is no evidence that the occlusive lipstick, deodorants, sun screens, hair products, and nail products suffocate lice and they have no pediculicidal or ovicidal effects.22 Kerosene or gasoline should never be used due to flammability and extreme Dry-on Suffocation-Based Pediculicide
hazard. Another "natural" remedy is Chick-Chack®, Nuvo® Lotion, or dry-on suffocation-based pediculicide containing coconut oil, anise oil, and ylang ylang (DSP) (later found to be Cetaphil® Gentle Skin Cleanser) oil.3 Published data is sparse and caution should be 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 Conclusion
was reported to work by suffocating the louses’ spiracles Lice have developed resistance to some pediculicides or breathing holes, causing death by suffocation. As and it is expected that with ongoing use these reviewed in The Lancet13 and other sources,14,15 the pediculicides will probably become less effective. study did not use proper methods of diagnosing lice, These products can still be used effectively to treat was anecdotal, and was not a well-designed randomized nonresistant lice. Resistance should be suspected if control study. Nevertheless, the concept is novel and live lice are still present 2–3 days after a product has there may be a significant beneficial effect; therefore 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 Nit Agents
certain. Resistant infections should be treated with Further knowledge of the nit sheath, the glue by which an agent from a different class of pediculicides or the egg is attached to human hair, or the nit laying process with newer non-neurotoxic agents. New products are may lead to the production of future treatment agents.19 presently in the process of being developed and tested. Over time these products may prove to be equal to Mechanical Removal
or more effective/safe than the standard neurotoxic Mechanical nit removal as a treatment modality is not an pediculicides, while at the same time minimize the appropriate method of lice eradication when used alone.20 problem of treatment resistant lice.
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 1. Hansen RC. Overview: the state of head lice mixture of white vinegar and water followed by combing management and control. Am J Manag Care 10(9 with a nit comb can aid in the removal of nits. Nit combing is the only treatment recommended for children < 2 years 2. Hansen RC, O’Haver J. Economic considerations of age. It is labor intensive and somewhat painful.21 associated with Pediculus humanus capitis infestation. Clin Pediatr 43(6):523-7 (2004 Jul-Aug).
Environmental Interventions
3. Elston DM. Drugs used in the treatment of pediculosis. Clothing, linen and towels should be decontaminated by J Drugs Dermatol 4(2):207-11 (2005 Mar-Apr). hot water washing (60°C) or dry-cleaned. Combs and 4. Frankowski BL. American Academy of Pediatrics brushes should be treated with boiling water, alcohol, guidelines for the prevention and treatment of head lice bleach, or soaked in a disinfectant solution (for example infestation. Am J Manag Care 10(9 Suppl):S269-72 (2004 Sep).
5. Leung AK, Fong JH, Pinto-Rojas A. Pediculosis capitis. All household members and close contacts should be J Pediatr Health Care 19(6):369-73 (2005 Nov-Dec).
examined and treated concurrently if infested; and the 6. Burkhart CG, Burkhart CN. Clinical evidence of lice school should be notified. Bedmates should be treated resistance to over-the-counter products. J Cutan Med prophylactically. Furniture disinfection is unnecessary Surg 4(4):199-201 (2000 Oct).
since head lice generally die within 1–2 days when 7. Meinking TL, Serrano L, Hard B, et al. Comparative in vitro pediculicidal efficacy of treatments in a resistant head lice population in the United States. Arch Dermatol Alternative Treatments
Naturopathic products including herbal shampoos, 8. Downs AM, Stafford KA, Harvey I, Coles GC. Evidence occlusive agents (e.g., mayonnaise, margarine, and for double resistance to permethrin and malathion in olive oil), kerosene or gasoline are largely unproven or head lice. Br J Dermatol 141(3):508-11 (1999 Sep).
Skin Therapy Letter • Editor: Dr. Stuart Maddin • Vol. 11 No. 10 • December 2006 - January 2007

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