503. More severe form of erythema multiforme, distinguishing characteristics, complications / EM Rx / How to diagnose pediculosis, Sx

October 25th, 2008
by reuben in .rash

lice

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Responses to “503. More severe form of erythema multiforme, distinguishing characteristics, complications / EM Rx / How to diagnose pediculosis, Sx”

  1. From Lex, WJEM, 2013:

    Pediculus capitis is a worldwide concern that affects persons of all socioeconomic backgrounds and ages, but it is most prevalent in children aged 3–13 years old. Since lice cannot fly or jump, transmission occurs through direct head- to-head contact, and possibly through the sharing of combs, hair brushes, or hats (although this is controversial). First-line treatments currently recommended by the American Academy of Pediatrics are the over-the-counter products, 1% permethrin or pyrethrins.

    Permethrin (Nix®) has low toxicity, can be used in children as young as 2 months of age, and does not have cross-sensitivity with plant allergies (a theoretical risk with pyrethrins, which are derived from chrysanthemum flowers) However, resistance to permethrin is well documented and may limit its usefulness in certain areas of the country.

    Pyrethrins (A-200, Licide, Pronto, RID, others) are neurotoxic to lice, but have little toxicity in humans. They
can only be used in children 2 years of age and older and may cause an allergic reaction in patients with ragweed sensitivity. Neither permethrin nor pyrethrins are 100% ovicidal, since newly laid eggs do not have a nervous system for several days. Each costs about $20 for pediculocidal doses.

    Product labeling of permethrin and pyrethrins recommends a second application at least 7 to 10 days after the initial application. Under average conditions, an egg or nit will hatch in approximately 8.5 days. Based on this time to hatch, a second treatment at 7 days will not be effective; some experts recommend the second treatment should we withheld until 9 to 10 days.

    Lindane is no longer considered a first-line agent, as there are many reports of resistance, and it may have central nervous system side effects in humans. It should only be considered if head lice are unresponsive to other therapies, and then only in patients who weigh at least 50 kg. Its use has been banned in California.34

    Malathion (Ovide®) is effective, but costs about $160. It is ovicidal, but the high alcohol content makes risk of accidental ingestion and flammability a concern. It is only approved for use in children 6 years of age and older, but resistance has not yet been proven in the U.S. (Malathion- resistance to lice is common in England.)

    Benzyl alcohol lotion (Ulesfia®, which costs about $160, depending on hair length) is a suffocation-based therapy for head lice. It avoids pesticide or neurotoxin use, and resistance is not a problem, since it suffocates the lice. It can be used in children as young as 6 months of age, but kills only lice, and not the nits, so a second application is necessary 10 days after the initial application.

    In the 12 years I have been doing this drug review, this will be the third unique product that I have reviewed for head lice. Topical ivermectin (Sklice®) is the newest product to be approved in the U.S. Ivermectin binds to glutamate chloride channels in nerve and muscle cells of lice, leading to an increased permeability to chloride ions resulting in paralysis and death. Based on this mechanism, it would appear that ivermectin is not ovicidal. But in vitro studies show that all lice hatched from eggs exposed to ivermectin died without the need for a second treatment. In addition, many of these lice were unable to suck blood, indicating that ivermectin somehow affected their ability to feed. One treatment costs approximately $260.

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