Permethrin is used for the topical treatment of pediculosis (lice infestation) and scabies (mite infestation). Permethrin has been used topically for prophylaxis of pediculosis capitis during head lice epidemics. In addition, the drug has been used topically for the treatment of other arthropod infestations (e.g., demodicidosis).
Permethrin is used for the topical treatment of pediculosis capitis (head lice infestation), and many clinicians consider it a pediculicide of choice. Permethrin has been used for prophylaxis of pediculosis capitis during head lice epidemics.
When selecting a pediculicide for the treatment of pediculosis capitis, clinicians should consider efficacy (including both pediculicidal and ovicidal activity), safety, cost, availability, ease of application, age of patient, presence of other scalp infections, patient preference, severity of the infestation, potential for transmission, number of recurrences, and the pattern of resistance in the geographic region. Although no pediculicide possesses true ovicidal activity, drugs with residual activity may kill emerging nymphs. The American Academy of Pediatrics (AAP) and others currently recommend use of topical permethrin 1%, topical malathion 0.5%, topical pyrethrins with piperonyl butoxide, topical crotamiton 10%, or oral ivermectin for the treatment of head lice infestations in the US.
Permethrin 1% generally is considered the treatment of choice and malathion 0.5% is recommended when permethrin resistance is suspected. Permethrin 1% has the advantages of a low potential for toxicity and good ovicidal activity; however, widespread resistance to permethrin has been reported in other countries and the prevalence of resistance to the drug in the US is unclear. Malathion 0.5% has the advantages of fast pediculicidal and ovicidal activity, a residual effect, and possible efficacy in lice infestations resistant to other pediculicides; however, safety and efficacy of the drug have not been established in children younger than 6 years of age, the topical preparation commercially available in the US has an alcoholic vehicle that is flammable and may be irritating, and the preparation has a characteristic odor that may impact patient preference. Some clinicians consider topical pyrethrins with piperonyl butoxide an alternative rather than a preferred treatment for pediculosis capitis since the drug has low ovicidal activity without residual activity (a second treatment 7-10 days after the first treatment usually is necessary to kill newly hatched lice) and treatment failures have been reported even when dosage and administration recommendations were followed. In the past, lindane was widely recommended for the treatment of pediculosis capitis; however, the drug is no longer recommend for initial therapy because of reports of resistance and neurotoxicity (e.g., seizures) and is now considered a second-line agent that should be used for the treatment of pediculosis only in patients who have not responded to or who cannot tolerate other recommended therapies.
If used correctly, one treatment with permethrin 1% usually is effective in eradicating pediculosis capitis. Some clinicians recommend a second treatment 7-10 days later to achieve maximum results, especially if the patient's hair is washed 7 days after initial treatment; however, the manufacturer recommends a second application only if live lice are observed 7 days or more after the first treatment. In resistant cases, some clinicians recommend use of permethrin 5% cream (left on overnight); use of permethrin 1% left on for a longer period of time (e.g., 30-60 minutes); or use of another drug (e.g., topical malathion 0.5%).
(See Pediculosis Capitis under Dosage and Administration: Dosage.)Alternatively, some clinicians recommend that resistant cases of head lice be treated with topical petrolatum (30-40 g left on overnight); however, the efficacy of such therapy with occlusive agents has not been evaluated to date.
Pediculicides kill lice quickly after application, therefore when living lice are detected during scalp inspection performed at least 24 hours after treatment, it is likely that the pediculicide was not applied correctly or that a very heavy infestation, reinfestation, or resistant infection exists. After incorrect pediculicide application is ruled out, the AAP recommends that such patients be immediately retreated with a different pediculicide, followed 7-10 days later by a second application.
Permethrin 1% lotion has been used for prophylaxis of pediculosis capitis during head lice epidemics. Such prophylactic use of permethrin 1% lotion should only be considered for individuals exposed to head lice epidemics in which at least 20% of the population at an institution is infested or for immediate household members of infested individuals. The manufacturer states that casual use of the drug is strongly discouraged.
In controlled studies, a single application of permethrin 1% lotion (cream rinse) generally has been at least as effective or more effective than lindane 1% shampoo or pyrethrins with piperonyl butoxide for the treatment of pediculosis capitis. However, comparative efficacy of pediculicides is difficult to evaluate because of factors related to the study populations and concerns that adherence to treatment regimens and reinfestation may impact clinical outcome. Most comparative clinical studies published to date have involved patients in other countries where resistance to other pediculicides may be widespread or in developing countries among patients with no previous exposure to pediculicides. It is unclear whether results of these studies are applicable to the US population.
In studies comparing permethrin 1% cream rinse and lindane 1% shampoo applied to adults and children with pediculosis capitis, cure (absence of live adult lice or nymphs during a 5-minute examination of the hair and scalp) was attained in over 97% of those treated with permethrin and in 67-85% of those treated with lindane within 14 days. When permethrin 1% was compared with pyrethrins with piperonyl butoxide, results of clinical studies have varied; some studies have shown that the treatments are both highly effective, while the results of another study indicated that permethrin was more effective (96% cured) than pyrethrins with piperonyl butoxide (62% cured). This difference may be due to study design differences; in one study where nits in the hair were not combed out and pyrethrins with piperonyl butoxide was applied only once (rather than the recommended 2 applications), its efficacy at 14 days was 62%. In studies where combing of nits was performed by evaluators, the efficacy of pyrethrins with piperonyl butoxide as either a single application or repeated in 7 days was similar or equal to that of permethrin.
Although there are few well-controlled, clinical studies of topical permethrin for the treatment of pediculosis pubis (pubic lice infestation), the US Centers for Disease Control and Prevention (CDC) and others consider topical permethrin 1% or topical pyrethrins with piperonyl butoxide to be the pediculicides of choice for the treatment of pediculosis pubis. Alternatives recommended by the CDC and others are topical malathion 0.5% or oral ivermectin. Topical malathion 0.5% may be effective for pediculosis pubis resistant to other pediculicides, but the drug is commercially available in an alcohol vehicle that is flammable and irritating and patients may find the drug's odor and longer duration of application objectionable. Although topical lindane 1% also has been recommended for the treatment of pubic lice, the drug is no longer recommended as initial therapy because of reports of resistance and neurotoxicity (e.g., seizures) and is now considered a second-line agent that should be used for the treatment pediculosis only in patients who have not responded to or who cannot tolerate other recommended therapies.
For infestation of the eyelashes with pubic lice, the CDC recommends treatment with an occlusive ophthalmic ointment (e.g., petrolatum) 2-4 times daily for 8-10 days; nits should be removed from the eyelashes manually. In addition to the pubic area and the eyelashes, pubic lice also may be found on other hairy areas of the body, including the eyebrows, mustache, beard, axilla, coarse hair of the back and trunk, perianal area, and, rarely, the scalp.
If used correctly, one treatment with permethrin 1% usually is effective in eradicating pediculosis pubis. Some clinicians suggest use of permethrin 5% for the treatment of pediculosis pubis. The CDC recommends reevaluating the patient 1 week after treatment if symptoms persist. The CDC recommends retreatment with an alternative regimen in patients who fail to respond to the initial regimen. However, some clinicians recommend routine retreatment of patients with pediculosis pubis using the same regimen 7-10 days after initial treatment.
Pediculosis pubis usually is transmitted by sexual contact. Presumptive concurrent treatment of sexual contacts to whom lice might have been spread within the last month is recommended. Patients should avoid sexual contact with their sexual partner(s) until patients and partners have been treated and reevaluated to rule out persistent disease. Presumptive concurrent treatment also has been recommended for other close contacts of the patient.
The CDC states that patients with human immunodeficiency virus (HIV) infection who have pediculosis pubis should receive the same treatment as those without HIV infection.
In a controlled study comparing single applications of permethrin 1% cream rinse or lindane 1% shampoo, followed by nit combing, in otherwise healthy adults, cure (absence of viable nymphs or adult lice) was obtained in 57% of those who received permethrin or 60% of those who received lindane. It was noted that the study population was predominantly male and homosexual, and reinfestation could not be excluded; other clinicians have confirmed the difficulty of successfully treating sexually active male homosexuals and their sexual contacts.
Permethrin 1% is used for the topical treatment of pediculosis corporis (body lice infestation). In some cases, body louse infestations may be treated by improving hygiene and by decontaminating clothes and bedding by washing at temperatures that kill lice. If the infestation is severe, a pediculicide should also be used (e.g., topical permethrin, topical pyrethrins with piperonyl butoxide, topical malathion, oral ivermectin).
Permethrin is used for the topical treatment of scabies. The American Academy of Pediatrics (AAP), CDC, and other clinicians consider topical permethrin 5% the scabicide of choice because of its safety and efficacy profile relative to other available agents; the CDC also recommends oral ivermectin as a scabicide of choice in adults. Recommendations for alternative therapy differ among various clinicians. The AAP and some clinicians recommend topical crotamiton 10% or oral ivermectin as preferred alternatives. Other clinicians recommend use of topical sulfur in infants younger than 2 months of age and in pregnant or lactating women, although it is less convenient since it must be applied on 2-3 consecutive days and some patients object to the drug because it is messy, malodorous, and tends to stain. Topical lindane 1% (not recommended in pregnant or lactating women, children younger than 2 years of age, or individuals with extensive dermatitis) is considered a second-line agent and should be used for the treatment of scabies only in patients who have not responded to or who cannot tolerate other recommended therapies.
If used correctly, one treatment with permethrin 5% usually is effective in eradicating scabies. Experts disagree on the need for retreatment; some experts recommend retreatment if symptoms persist after 1-2 weeks, while others recommend retreatment only if live mites are observed. Still others recommend routine retreatment (i.e., 2 courses), particularly in severe cases with diffuse cutaneous findings. The CDC recommends retreating patients who do not respond to permethrin with an alternative regimen. Pruritus associated with scabies usually is not considered an indication for retreatment; such pruritus results from a hypersensitivity reaction of the host to the mite and may persist for several weeks despite successful treatment. Oral antihistamines and topical corticosteroids may be used to help relieve symptoms. Many clinicians recommend follow-up examinations of patients 2 and 4 weeks after treatment. If the patient is not clear of new lesions at either examination, it should be considered a treatment failure; such treatment failures may be secondary to failure to treat all exposed individuals or failure to apply the drug properly. If the patient is clear of new lesions when examined at 2 weeks, but has new lesions at 4 weeks, it should be considered a reinfestation rather than a treatment failure.
In less than 10% of patients with scabies, nodular scabies may develop, which is characterized by intensely pruritic nodules that persist for months after effective scabies therapy; mites seldom are identified in these nodules. Scabicide therapy usually is ineffective in nodular scabies since mites are not typically present. Topical or intralesional corticosteroids may be useful to treat the pruritus associated with nodular scabies.
Mild infections secondary to scabies usually remit, but concurrent systemic anti-infective therapy may be necessary for severe secondary infections.
Sexual contacts and other individuals (household, family) who have had close personal contact with a patients with scabies within the previous month should be examined and treated. Manifestations of scabies (e.g., pruritus, erythema, skin lesions) are the result of hypersensitivity to the mite and its eggs and waste products, and manifestations usually are not evident until 1-2 months after infestation in individuals without previous exposure. Therefore, the absence of symptoms in individuals in close contact with a patient with scabies should not be interpreted as an absence of infection; failure to treat such individuals may result in reinfestation of the patient.
The CDC recommends that scabies epidemics in institutional settings (e.g., nursing homes, hospitals, residential facilities, communities) be managed in consultation with an expert. Control of such epidemics requires treatment of the entire population at risk. Permethrin has been recommended as a scabicide of choice in institutional outbreaks. Oral ivermectin may be useful in this setting, especially if treatment with topical scabicides fails. In one study, topical permethrin 5% cream produced an overall cure rate of 98% in the residents, staff, and frequent visitors of 3 nursing homes with scabies epidemics that had not responded to other topical scabicides (e.g., lindane, crotamiton, benzyl benzoate, precipitated sulfur), although some patients required 3 or more treatments.
Norwegian scabies (crusted scabies) is a particularly severe and highly infectious form of scabies that presents as crusted, hyperkeratotic, scaling plaques, which may be generalized or localized to the hands and feet. In this condition, the patient is infested with large numbers (thousands to millions) of Sarcoptes mites. Norwegian scabies is highly contagious and, because the infestation may have an atypical presentation, months to years may pass before the condition is diagnosed, and transmission of scabies to personal contacts may occur before symptoms of scabies develop in the index patient.
Patients with Norwegian scabies often require multiple treatments with scabicides, and it is important that the total body, including areas under the nails, be treated when topical therapy is used. Permethrin has been used to treat Norwegian scabies with good results. However, sequential use of several different scabicides may be necessary. Some clinicians pretreat patients with a keratolytic agent before using a topical scabicide. Other clinicians recommend therapy with a topical scabicide in conjunction with oral ivermectin or multiple doses of oral ivermectin. Some clinicians consider oral ivermectin the therapy of choice for patients whose infection is refractory to topical therapy; however, the comparative efficacy of ivermectin and standard scabies therapies remains to be established. Norwegian scabies results in extensive skin excoriation and requires heavy topical scabicide application, therefore lindane 1% is not recommended because of the increased risk of toxicity.
The CDC states that patients with HIV infection who have uncomplicated scabies should receive the same treatment as those without HIV infection. Other clinicians recommend that 2 courses (1 week apart) of permethrin 5% routinely be used for treating scabies in patients with HIV infections. Alternatively, weekly treatment until symptoms and lesions clear has been recommended. Treatment with lindane 1% or sulfur 5% ointment also has been recommended for the treatment of scabies in patients with HIV infection.
HIV-infected individuals and other immunocompromised patients are at increased risk of developing Norwegian scabies, and the CDC recommends that such patients be managed in consultation with an expert. Some clinicians recommend oral ivermectin for immunocompromised patients whose scabies is refractory to topical therapy.
Results of several controlled studies in otherwise healthy adults and children with scabies indicate that topical permethrin 5% cream is as effective as, or in some cases, more effective than topical lindane 1% lotion. However, in some cases the lower efficacy of lindane may be related to resistance secondary to widespread use of the drug in the treatment of scabies and pediculosis. Cure (healing of old lesions and an absence of new lesions) was attained 3-4 weeks after treatment in 91-100% of patients who received permethrin 5% and in 65-92% of those who received lindane 1%. In a controlled study in a community in which scabies had been endemic for over 10 years, single application of permethrin 5% cream or lindane 1% lotion to otherwise healthy children and adults cured 91% of patients who received permethrin and 65% of those who received lindane. In this study, 9 patients judged as treatment failures (8 of whom had received lindane) were retreated with permethrin and were cured in 2-3 weeks. However, the low efficacy of lindane in this study may have been related to widespread use of the drug in the area resulting in increased resistance, since cure of scabies after lindane treatment was achieved in 90% of patients in nearby communities not previously exposed to lindane.
In a comparative study evaluating topical permethrin 5% cream and topical crotamiton 10% cream administered once daily on 2 successive nights in children and adults, 98% of patients who received permethrin and 88% of those who received crotamiton were cured (no new lesions and healing of all original lesions) 4 weeks after treatment. In a double-blind, randomized study comparing single applications of topical permethrin 5% cream and crotamiton 10% cream in children 2 months to 5 years of age, 89% of patients who received permethrin and 60% of those who received crotamiton were cured (no new lesions and healing of all original lesions). In an open study comparing a single topical application of permethrin 5% (2.5% for children younger than 5 years of age) cream with topical benzyl benzoate 20% (10% for children younger than 5 years of age) applied on 3 successive nights, all patients in both groups were cured.
Topical permethrin has been used to treat infestations with Demodex folliculorum in children and adults and D. brevis in children, including patients with immunosuppression (e.g., acquired immunodeficiency syndrome, acute lymphoblastic leukemia). The role of Demodex as a pathogen in human disease is controversial, and some clinicians consider Demodex a normal inhabitant of the skin that generally does not cause clinical disease in humans since the mite has been found in normal biopsies without any inflammation or evidence of disease. Other clinicians suggest that alterations in the immune system may allow the mite to proliferate to the extent that clinically evident disease occurs. Topical treatment with permethrin 1% or permethrin 5% have been used successfully for the treatment of demodicidosis, although failures also have been reported. Some clinicians note that it is not certain how much permethrin penetrates into the follicle and what effect, if any, the drug has on D. follicularis or D. brevis. Additional study and experience are needed to evaluate fully the efficacy of permethrin and the optimum regimen, if any, for the treatment of demodicidosis.