IVERMECTIN: A New Treatment Option for Resistant Scabies and Head Lice

Two of the most common infestations confronting the health care volunteer working in developing countries are scabies and head lice. Although neither is life threatening, both can cause significant discomfort and at times interfere seriously with quality of life.
Scabies is caused by the invasion of an almost microscopic mite into the skin, where it completes its life cycle. The most common sites are usually on the hands and arms, but can involve the entire body in small children and debilitated or aged adults. After some time the host develops an allergic very itchy rash, which more quickly recurs with re-infection. A number of treatments have been used. Lindane lotion is effective, but has fallen into disuse because of concerns about neurotoxicity. Permethrin cream is currently the most widely prescribed, but treatment failures and recurrences are common. Oral Ivermectin, widely used as a vermifuge, has been successfully used in a number of trials as a single dose of 200-400 micrograms/kg, repeated after one week. Success rates of 95% have been reported, even in cases of treatment failure with other approaches or difficult to treat cases of extensive generalized scabies.

Head lice have posed somewhat similar treatment difficulties. Lindane shampoo is no longer recommended. Permethrin 1% cream has been effective in the past, but is showing increased resistance. A recent study showed that ivermectin at a dose of 400 micrograms/kg repeated after one week in combination with nit combing resulted in a 97% clearance rate at 15 days, far superior to any other treatment regimen.

Ivermectin is currently available as 3 and 6 mg tablets. Only the brand name Stromectol is currently available for purchase in the US and is prohibitively expensive at around $6 per 3mg tablet. However, mission supply houses such as Blessings International have generic ivermectin available to health care volunteers for overseas use only, at about 20 cents per 6 mg tablet. Although ivermectin is not currently FDA approved for the treatment of either scabies or head lice, it is becoming more widely used throughout the world for this purpose. The side effect profile is low. It seems prudent for us to continue to use permethrin for the routine treatment of uncomplicated infestations with scabies and head lice, particularly in small children and women who are pregnant or breast feeding. Ivermective can be considered as a viable, safe alternative in cases of treatment failure, for institutional epidemics where mass local treatment is impractical, or for massive infection in immuno-compromised patients.

Submitted by Roger Boe, M. D.

References

1. Currie, B.J. et. Al. Permethrin and Ivermectin for Scabies. N. Engl. J Med 2010; 362: 717-725.

2. Chosidow, O. et. Al. Oral Ivermectin versus Malathion Lotion for Difficult-to Treat Head Lice. N. Engl. J Med 2010; 362: 896-905.

3. Boe, R. W. Scabies: An Update on Treatment; www.umvim4health blogspot.com 2009.

Scabies: An Update on Treatment

Scabies is a skin infestation caused by an almost microscopic mite, Sarcoptes scabei. Although distribution is worldwide, scabies occurs more frequently in tropical resource poor countries. The life cycle is completed entirely on the human host. The gravid female mite burrows into the top layer of skin to lay her eggs. The larvae hatch, reach the skin surface, mate and complete the cycle. Transmission is by skin-to-skin contact, and is most likely within families, in institutions or schools, or by sexual contact. The initial infestation is asymptomatic for approximately one month. Then an intense inflammatory immune mediated reaction occurs, associated with intense persistent itching, which is the major hallmark of the condition. Re-infection produces a more immediate reaction within 48-72 hours. Other characteristic findings are the presence of a linear burrow (which is often obscured by excoriation) and a distribution pattern of lesions on the webs of fingers, the wrists, the axillae, and on the genitalia in the case of sexual contact. Infants are more likely to have a generalized body rash. If infection occurs in an immunocompromized or elderly person, a particular pattern of generalized rash occurs with thick scaling. Called Norwegian scabies, this variety involves thousands of mites in contrast to the 10-50 found in the usual adult infestation, and is highly contagious. The diagnosis of scabies can be established by microscopic examination of skin scrapings for eggs or mites, but is more commonly made by the characteristic pattern of lesions, the presence in other family members or close contacts, and the presence of intense itching. Institutional epidemics can occur.
A number of treatment options are available. Thorough cleaning and heat drying of bed clothing is indicated, as the mite may survive for as long as 3 days away from the host. A 10% sulfur in petrolatum ointment, which is over the counter, has been used for many years. It is safe to use in small infants. It is messy, requires repeat applications, and is less effective than more recently introduced agents. Benzoyl benzoate is moderately effective but not available in the US. Lindane (Kwell) lotion is no longer widely used because of concerns about neurotoxicity, and may be difficult to obtain. It should not be used in children or pregnant women. A 5% permethrin cream (Elimite) has recently been the topical treatment of choice. The cream is applied to the entire body except the face and washed off after 8 hours. A second treatment is applied after one week. Permethrin is non-toxic, and can be used in children as young as two months of age. It is not recommended for pregnant women. Recently Ivermectin, which has been widely used as a vermifuge, has been found to be highly effective and safe in treating scabies, in a single dose of 200 micrograms per kilogram. It is not currently FDA approved, however, for this use. Therefore it is prudent to continue to use permethrin cream as the first line treatment. Ivermectin can be considered in cases of treatment failure, with institutional epidemics where mass local treatment is impractical, or for massive infection in immunocompromized patients, the so-called Norwegian or crusted scabies.
1. Leme PA. Scabies and Pediculosis pubi, an Update of Treatment Regimens and General Review. Clinical Inf. Disease, 2007:44: s153-59.
Fawcett R. Invermectin Use in Scabies. Am. Fam. Physician, 2003: 68:1089-92.
Roger Boe MD