eMedicine Specialties > Dermatology > Parasitic Infections
Lice: Treatment & Medication
Updated: Sep 4, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Treatment
Medical Care
Reinfestation occurs unless louse infestation is addressed as a community-wide problem. Management must include examination of all individuals exposed and treatment of all those who are infested. Education has been shown to reduce the number of lice infestations in schools. "No nit" policies exclude many children from the classroom, but they have not been shown to reduce the number of lice infestations.8
Fomite control is essential. Hats lined up on pegs or placed in adjacent cubbyholes provide an avenue for spread of the infestation. Cubbyholes can be sprayed with a permethrin spray or other insecticide, but the most effective method is for each child to "ground his or her clothing" (ie, hat, coat, scarves) under each individual chair or desk. Common cloakrooms may suggest an antiquated charm, but they should be viewed as merely antiquated and a site for spread of the infestation.
Combs, brushes, and headbands should not be shared. Shaving of hair is effective but not socially acceptable in most societies.9 Young nits do not have a nervous system and are immune to neurotoxic pediculicides.
Nit combs are provided with many products. Metal nit combs are more effective and can be purchased through the Internet. Chemical nit removers, such as distilled white vinegar and formic acid (GenDerm Step 2), can be helpful. An enzymatic nit remover (Clear) is also available, but the major action of each of these products may be to make combing easier. Little evidence indicates that they actually dissolve the nit sheath that attaches the nit to the hair shaft. Advances in topical therapy will include lotions that specifically dissolve the attachment of the nit to the hair.10
For body lice, when feasible, removal of infested clothing is all that is required. Laundering in hot water, ironing with a hot iron, or drying in hot dryer also is effective. In mass epidemics, other treatments may be more practical. Body lice may respond to oral or topically applied pediculicides. None of these agents currently is labeled or marketed for treatment of body lice in the United States. Topical agents should be applied to clothing, especially the seams. Published data suggest that permethrin spray can help prevent body lice reinfestation.
In some cultures, monkeys are used as patient nit pickers to groom the hair and to remove adult lice and nits.
Resistance to pediculicides is emerging.11,12,13,14 In the United States, malathion retains the best efficacy among chemical pediculicides at present. Permethrin appears to have a wide margin of safety, although some data suggest a possible connection between insecticides and leukemia.15,16 Better agents that work via clogging of respiratory spiracles rather than via neurotoxicity would be valuable additions to the armamentarium.17,18 Valuable adjunctive treatments include wet combing and forced air. One such agent is benzyl alcohol lotion, which was recently approved by the US Food and Drug Administration.
The safety and effectiveness of benzyl alcohol lotion 5% was demonstrated in 2 multicenter, randomized, double-blind studies of 628 people, aged 6 months and older, with active head lice infestation. Individuals received two, 10-minute treatments of either benzyl alcohol lotion or topical placebo, 1 week apart. When observed 2 weeks following the final treatment, more than 75% of those treated with benzyl alcohol lotion were lice free compared with the placebo vehicle (4.8-26.2%).19
Desiccation of lice is possible with forced air, but this process takes roughly 30 minutes. Combing regimens must be repeated frequently over a period of days.20 Various botanical agents have been used. Essential oils demonstrate variable efficacy and may be contact allergens.21 In general, the evidence supporting their efficacy is of poor quality.22,23 Dimethicone and monoterpenoids are promising agents.22,24,25
Related clinical guideline summaries include the following:
- British Association for Sexual Health and HIV - United Kingdom national guideline on the management of phthirus pubis infestation26
- Centers for Disease Control and Prevention - Ectoparasitic infections. Sexually transmitted diseases treatment guidelines 200627
- University of Texas, School of Nursing, Family Nurse Practitioner Program - Guidelines for the diagnosis and treatment of pediculosis capitis (head lice) in children and adults 200828
Medication
Pediculicides
Treatment options include Malathion, permethrin cream, and pyrethrins. Less toxic agents (eg, benzyl alcohol lotion) are being developed or are now FDA-approved that aim to occlude the respiratory spiracles of the louse and kill via asphyxiation.29 Reports suggest the possibility of neurotoxicity from ivermectin in a population of nursing home patients treated for scabies.30,31,32,33,34
Permethrin (Nix, Elimite)
DOC recommended by most authorities. Resistance probably has developed in many areas. Physicians in some countries select different pediculicides on a rotating basis to discourage development of resistance. Very effective in killing adult lice and nymphs but not as effective in killing nits (eggs). OTC 1% concentration may be insufficient for treatment of pubic lice and for some cases of head lice. The 5% prescription preparation marketed for scabies (Elimite) may be more effective in some cases. One benefit of permethrin is a residual effect in the hair for several hair wash cycles.
Adult
Wash hair with nonmedicated shampoo; apply as cream; leave in place for 10 min, then rinse off; unless every nit is removed, may apply second application 7-10 d after initial therapy
Pediatric
Administer as in adults
Enzymatic nit removal systems may inactivate permethrin (use before, not after, permethrin)
Documented hypersensitivity
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
May exacerbate redness, swelling, and itching, at least temporarily
Pyrethrins (RID Mousse, RID Shampoo, A200, Barc)
Treatment of P humanus infestations. Stimulates nervous system, causing seizures and death of parasite. Older OTC agent that still appears effective. Lacks residual action of permethrin.
Adult
Wash hair with nonmedicated shampoo; apply as cream; leave in place for 10 min (or apply overnight), then rinse off; unless every nit is removed, may apply second application 7-10 d after initial therapy
Pediatric
Administer as in adults
None reported
Documented hypersensitivity to ragweed or turpentine; actual incidence of cross-reaction is uncertain, but many other agents are available
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Do not apply to eyes, face, or mucous membranes; retreatment in 7-10 d necessary to kill newly hatched nymphs
Fluorescein dye strips (SoftGlo Strips)
Used with white petrolatum. Helpful in the management of eyelash nits. Dye strips are used as if looking for a corneal abrasion (off-label use).
Adult
Apply to eyelashes 3 successive nights, and wash 24 h after each application
Pediatric
Administer as in adults
None reported
Documented hypersensitivity
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Petrolatum obscures vision but is safe and useful in young infants
Ivermectin (Stromectol)
Used in mass epidemics of lice and scabies. Few serious adverse effects have been reported when drug is used to treat lice or scabies. Not associated with evidence of selective fetotoxicity in pregnant women inadvertently exposed (based on limited data). Limited animal data also fail to show evidence of selective fetotoxicity. Available in United States as oral 6-mg pill marketed for treatment of Strongyloides. Physicians have used drug for lice and scabies (off-label use) in cases where such therapy was in the best interest of patients and conventional therapy failed. Health care providers in the United States are encouraged to read FDA statement concerning off-label use of approved drugs, which appears in the PDR.
One report suggests the possibility of neurotoxicity from the drug in population of nursing home patients treated with ivermectin for scabies. Patients also had been treated with other neurotoxic agents (eg, lindane). An unexplained decrease occurred in death rate on other wards that coincided with unexplained increase in death rate on the ward where ivermectin was used. Several authors have questioned whether deaths in this report had any real relationship to ivermectin. Health care providers are referred to articles and letters cited in the list of references.
Adult
150-200 mcg/kg/d PO as single dose; 12 mg PO repeated in 7-10 d
Pediatric
<5 years: Not established
>5 years: Administer as in adults
May interact with other ligand-gated chloride channel (eg, those gated by GABA)
Documented hypersensitivity
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Treat those who intend to breastfeed only when risk of delayed treatment outweighs possible risks to the newborn caused by ivermectin excretion in milk; repeat courses of therapy may be required in immunocompromised patients; may cause nausea, vomiting, mild CNS depression, and drowsiness
Malathion (Ovide)
Approved by US FDA in 1999 to treat head lice. Irreversible cholinesterase inhibitor that is hydrolyzed (and therefore detoxified) rapidly by mammals but not by insects; ovicidal and pediculicidal. Binds to hair, and provides some residual protection after therapy. Used as a 0.5% lotion and 1% shampoo for pediculosis and scabies.
Adult
Apply copious amounts of lotion to dry hair and massage; leave on 8-12 h, rinse, and remove nits with fine-tooth comb (repeat in 7-10 d if lice present)
Pediatric
<2 years: Not recommended
>2 years: Administer as in adults
None reported; potential for interaction with aminoglycosides and antimyasthenics
Documented hypersensitivity
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
Contains flammable alcohol, so do not expose lotion or wet hair to open flame or electric heat, such as hair dryer (allow hair to dry naturally and uncovered following application); avoid contact with eyes (flush eyes immediately with water if contact occurs)
Benzyl alcohol lotion
Benzyl alcohol inhibits lice from closing their respiratory spiracles, allowing the lotion to obstruct the spiracles, which ultimately results in asphyxiation. Does not elicit ovicidal activity. Contains 5% benzyl alcohol.
Adult
Apply lotion to dry hair, using enough to completely saturate scalp and hair; rinse off with water after 10 min; repeat treatment in 1 wk
Pediatric
<6 months: Do not use
>6 months: Apply as in adults
None reported
Documented hypersensitivity
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
May cause irritation to skin, scalp, and eyes (avoid eye exposure and flush immediately with water if contact occurs); application site anesthesia and hypoesthesia may occur; serious adverse events (eg, respiratory distress, seizure, coma) and death with benzyl alcohol have been well documented in premature infants; IV administration of products containing benzyl alcohol has been associated with neonatal gasping syndrome consisting of severe metabolic acidosis, gasping respirations, progressive hypotension, seizures, CNS depression, intraventricular hemorrhage, and death in preterm, low birth weight infants; neonates (ie, <1 mo or preterm infants with a corrected age <44 wk) could be at risk for gasping syndrome if treated
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Further Reading
Keywords
lice, lice infestation, pediculosis, louse infestation, nits
