Pediculosis

Introduction

A lice infestation (pediculosis) is a parasitic infestation of the skin of the scalp (head lice), trunk (body lice) or pubic areas (crab lice). Lice are small, wingless parasites with reasonably well-developed legs. Lice infestations are common among all social groups in the United States, affecting about 10 million Americans annually.12 They appear to peak in children a few weeks after school starts each fall (August through November), after extended vacations and after camps. They are also common in daycare centers and nursing homes.1'2 Children are more likely than adults to acquire lice, and preschoolers are at highest risk. Girls tend to get infected at a higher rate than boys, and whites get infected at higher rates than African Americans. 1,2

Source of Infection

Head lice are commonly transmitted by shared use of caps or combs and are epidemic among children of all socioeconomic levels, especially in elementary schools. Adults with head lice almost always acquire the infection from school-age children. Body lice generally occur in people who live in overcrowded dwellings with inadequate hygiene facilities. Pubic lice can be acquired by sexual transmission, shared toilets, etc.

Three different varieties of lice are generally involved:

1. Pediculus humanus var. capitis is associated with head lice.

2. Pediculus humanus var. corporis is associated with body lice.

3. Pthirus pubis is associated with pubic lice or "crabs."1

Head and body lice are very similar in appearance, about 3 to 4 mm long; but body lice are larger. Head lice can be observed on the scalp, but body lice are seldom observed on the body; generally, they are on the clothing or in the seams of clothing and only go to the body to feed.

Infestations of body lice often occur in individuals who do not change clothing frequently, such as the homeless, or in soldiers in extended military campaigns. The body louse can also transmit trench fever, relapsing fever and typhus where these diseases are endemic.

The pubic louse, commonly called a crab louse because of its crablike appearance, can be encountered in all levels of society It is evidenced by the presence of the parasite, and its nits (eggs) are generally in the pubic area. Pubic louse infestations may actually be generalized, especially in hairy individuals; and the lice can also be found on the eyelashes, eyebrows, mustache, beard and scalp.

Clinical findings with head lice involve itching, and the lice can be observed crawling or as small nits attached to a hair shaft, resembling a bud on a leaf, close to the skin, especially above the ears and on the nape of the neck. It is actually difficult to observe a crawling head louse. Body louse infestations include symptoms of itching and associated scratching, which may result in excoriations, especially over the upper shoulders backside and neck. Pubic louse symptoms also include itching, The itching in these lice infections results from the bite of a louse, which causes an immediate wheal to develop around the bite. Lice may feed up to five or six times daily. If itching is se were, subsequent scratching may result in excoriation and/or secondary pyogenic infection.

Treatment

The goals of treatment include ridding the infested patient of the lice and preventing future lice infestations by avoiding direct physical contact with infested individuals and personal items, eg, combs, brushes, towels, caps, hats.

Treating lice is difficult due to the ease of spread. Individuals can usually be effectively treated; but, upon reexposure, they often become reinfected. Over the years, this repeated reexposure has resulted in resistance to the permethrins and a search for new treatment alternatives for louse infestations. Malathion remains a widely used compounded treatment; and, recently, ivermectin has been prescribed.2-4 For general treatment regimens, see sidebars. 1-4

Consider the following when treating lice infestations:

1. Use appropriate topical agent, and treat all members of the family.

2. Use hot water to wash brushes, combs and toys; dry items with hot air.

3. Use hot water to wash clothing; dry with hottest dryer setting.

4. For clothing that cannot be washed (coats, etc.), seal in plastic bags for at least 2 weeks (the life cycle of a louse when unable to feed on a host).

5. Schedule follow-up visit with physician, pharmacist or school nurse.

Preventing Lice Infestations

To help prevent lice infestations, avoid direct physical contact with infested individuals; and do not share personal articles, such as combs, brushes, towels, hats, caps, etc.

Pediculicides

Ivermectin is a mixture of various components and occurs as a white or yellowish-white, slightly hygroscopic, crystalline powder. It is practically insoluble in water and soluble in alcohol.4

Permethrin (C^sub 21^H^sub 20^O^sub 3^, MW 391.3) is a pyrethroid insec ticide used as a 1% application in the treatment of head lice. Permethrin is generally more effective than synergized pyrethrins.4

Malathion (C^sub 10^H^sub 19^O^sub 6^PS^sub 2^, MW 330.4) occurs as a clear, colorless or slightly yellowish liquid that solidifies at about 3 deg C. It is slightly soluble in water and miscible with alcohol and vegetable oils. Lotions are generally preferred to shampoos, as the contact time is longer.4

Pyrethrums (Pyrethrin I and Pyrethrin II) occur as a viscous, brown, liquid oleoresin that is obtained from chrysanthemum flowers. They are practically insoluble in water and soluble in alcohol. They can be absorbed through the skin. Pyrethrins are used in concentrations of from 0.17 % to 0.33 %, generally in combination with 2% to 4% piperonyl butoxide. Dosage forms include solutions, shampoos and gels.2,4,5

Piperonyl butoxide (C^sub 19^H^sub 30^O^sub 5^, MW 338.4) occurs as a yellow or pale brown oily liquid with a faint characteristic odor. It is very slightly soluble in water and miscible with alcohol. It is used as a synergist for pyrethrin and pyrethroid insecticides. Mixtures of pyrethrins and piperonyl butoxide are used in the treatment of lice infestations.4

Formulations for the treatment of lice infestations are shown in Table 1.

References

1. Tierney LM Jr, McPhee SJ, Papadakis MA. Current Medical Diagnosis & Treatment. New York:Lange Medical Books/McGraw-Hill; 2003:130-133.

2. Pray WS. Nonprescription Product Therapeutics. 1st ed. Baltimore:Lippincott Williams & Wilkins; 1999:462-469.

3. Mumcuoglu KY, Miller J, Rosen LJ et al. Systemic activity of ivermectin on the human body louse. J Med Entomol 1990;27:72-75.

4. Sweetman SC, ed. MARTINDALE The Complete Drug Reference. 33rd ed. London:Pharmaceutical Press; 2002:99-101, 1434-1436.

5. [No author listed.] The Merck Index. 3th ed. Whitehouse Station, NJ:Merck & Co., Inc.; 2001:1425.

Copyright International Journal of Pharmaceutical Compounding Sep/Oct 2003
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