Permethrin is a synthetic pyrethroid used primarily as a topical scabicide and pediculicide. Permethrin is a synthetic mixture of cis- and trans- isomers of pyrethrin chemically altered have more light and heat stability versus the natural pyrethrins. Permethrin is a commonly used agricultural pesticide and insect repellent; as a drug it is considered the treatment of choice for pediculosis capitis (head lice infestation). When used to treat head lice, a single application of 1% permethrin lotion is associated with a 97-99% cure rate; this cure rate is higher than that following application of 1% lindane. Permethrin is also better tolerated than lindane therapy. However, resistance to permethrin has been documented in several countries, including Argentina, Czech Republic, France, Israel, and the United Kingdom. In 1986, permethrin 1% lotion (Nix(R)) was approved by the FDA as a prescription drug for the treatment of head lice; this product was subsequently reclassified to nonprescription (OTC) status. Permethrin 1% lotion is also approved for head lice prophylaxis (see Dosage). Permethrin-based lice control sprays are available, but these are used to spray inanimate objects and are not for topical use on humans. In September 1989, a higher strength permethrin 5% topical cream (Elimite(R)) was approved by the FDA as a prescription drug for the treatment of scabies.
General Administration Information
For storage information, see the specific product information within the How Supplied section.
Route-Specific Administration
Topical Administration
-Permethrin is administered topically. Avoid getting into the eyes. Do not ingest.
-For proper treatment of pediculosis, nits (eggs) should be removed with a nit comb. Also, all personal headgear, scarfs, coats, and bed linen should be disinfected by machine washing in hot water and drying using the hot cycle of a dryer for at least 20 minutes. Personal articles that cannot be washed may be dry-cleaned, sealed in a plastic bag for 4 weeks, or sprayed with a product specifically designed for this purpose. Personal combs and brushes may be disinfected by soaking in hot water (above 130 degrees F) for 5 to 10 minutes.
Cream/Ointment/Lotion Formulations
-Elimite topical cream: For the treatment of scabies, thoroughly massage cream into the skin from the head to the soles of the feet. Remove by washing after 8 to 14 hours.
Other Topical Formulations
-Nix Creme Rinse: Shake well before using. For the treatment of head lice, apply a sufficient amount to saturate the hair and scalp, especially behind the ears and on the nape of the neck. Leave on hair for 10 minutes. Then, rinse thoroughly with water.
Scabies and pediculosis is often accompanied by pruritus, edema, and erythema. Treatment with permethrin may temporarily exacerbate these conditions. Permethrin may also cause mild burning and/or stinging. In patients treated with 5% permethrin cream, skin irritation (mild and transient burning and stinging) occurred in about 10% of patients and was associated with the severity of infestation. Pruritus was reported in 7% of patients at various times post-application. Erythema, hypoesthesia, tingling, and rash (unspecified) were reported in 1-2% of patients.
Use permethrin with caution in patients with hypersensitivity to other synthetic pyrethroids or pyrethrins, or to chrysanthemums. Many veterinary or household insecticides contain permethrin or other synthetic pyrethroids. Thus, permethrin should be used with caution in patients sensitive to these insecticides.
In cases of pediculosis capitis, self-medication of permethrin is not recommended if infestation of the eyebrows or eyelashes occurs. A physician should be consulted in these situations.
Permethrin was not mutagenic when evaluated in several in vitro and in vivo genetic toxicity studies.
Permethrin-containing products are for external use only. In the event of ocular exposure, immediately flush eye with water.
Safe and effective use of permethrin has not been established in neonates or infants less than 2 months of age.
Permethrin is classified as pregnancy category B. Reproductive studies in animals revealed no evidence of impaired fertility or harm to the fetus. However, there are no adequate and well-controlled studies in pregnant women. Thus, permethrin should be used during pregnancy only if clearly needed.
It is not known if permethrin is excreted in human milk. However, absorption of permethrin from the skin is minimal, and it is rapidly metabolized to inactive metabolites. Guidelines recommend permethrin for use in breast-feeding patients with lice and scabies. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, healthcare providers are encouraged to report the adverse effect to the FDA.
Per the manufacturer, this drug has been shown to be active against most strains of the following microorganisms either in vitro and/or in clinical infections: Pediculus capitis, Sarcoptes scabiei
NOTE: The safety and effectiveness in treating clinical infections due to organisms with in vitro data only have not been established in adequate and well-controlled clinical trials.
This drug may also have activity against the following microorganisms: Phthirus pubis
NOTE: Some organisms may not have been adequately studied during clinical trials; therefore, exclusion from this list does not necessarily negate the drug's activity against the organism.
For the treatment scabies infection, including crusted (Norwegian) scabies*:
-for the treatment of scabies infection:
Topical dosage (Permethrin 5% cream):
Adults: Massage 5% topical cream into the skin from the head to the soles of the feet. Scabies rarely infests the scalp of adults, although the hairline, neck, temple, and forehead may be infested in geriatric patients. Usually 30 grams is sufficient for the average adult. Wash cream off after 8 to 14 hours. One application is generally curative. Although pruritus may persist after treatment, this is rarely a sign of treatment failure and is not an indication for retreatment. Retreatment is indicated if living mites persist after 7 to 14 days of initial treatment.
Infants, Children, and Adolescents 2 months to 17 years: Massage 5% topical cream into the skin from the head to the soles of the feet. Wash cream off after 8 to 14 hours. One application is generally curative. Although pruritus may persist after treatment, this is rarely a sign of treatment failure and is not an indication for retreatment. Retreatment is indicated if living mites persist after 7 to 14 days of initial treatment.
-for the treatment of crusted (Norwegian) scabies* infection:
Topical dosage (Permethrin 5% cream):
Adults: Apply a full body application (all body parts from neck down) of permethrin 5% cream topically daily for 7 days and then 2 times weekly until cure in combination with oral ivermectin. Retreatment 2 weeks after the initial treatment regimen can be considered for those persons who are still symptomatic or when live mites are observed. Use of an alternative regimen is recommended for those persons who do not respond initially to the recommended treatment.
For the treatment of pediculosis:
-for the treatment of pediculosis capitis (head lice infestation):
Topical dosage (lotion):
Adults: Shampoo hair with regular shampoo, rinse and towel dry. Then, apply permethrin 1% lotion sufficient to saturate the hair and scalp (usually 25 to 30 mL), especially behind the ears and on the nape of the neck. Leave on hair for 10 minutes but no longer. Then, rinse thoroughly with water. Retreatment is required in less than 1% to 2% of patients. If live lice are seen 7 days or more after the first application, a second treatment should be given.
Infants, Children, and Adolescents 2 months to 17 years: Shampoo hair with regular shampoo, rinse and towel dry. Then, apply permethrin 1% lotion sufficient to saturate the hair and scalp (usually 25 to 30 mL), especially behind the ears and on the nape of the neck. Leave on hair for 10 minutes but no longer. Then, rinse thoroughly with water. Retreatment is required in less than 1% to 2% of patients. If live lice are seen 7 days or more after the first application, a second treatment should be given.
-for the treatment of pediculosis pubis*:
Topical dosage (cream):
Adults: Apply 1% cream topically to affected areas and washed off after 10 minutes. Patients should be evaluated 1 week after therapy and retreatment may be necessary.
For pediculosis prophylaxis:
NOTE: Prophylaxis is only recommended for individuals exposed to head lice epidemics in which at least 20% of the population at an institution are infested and for immediate household members of the infested individuals.
Topical dosage:
Adults, Adolescents, Children, and Infants >= 2 months: Shampoo hair with regular shampoo, rinse and towel dry. Then, apply topical permethrin 1% lotion sufficient to saturate the hair and scalp (usually 25 to 30 mL), especially behind the ears and on the nape of the neck. Leave on hair for 10 minutes but no longer. Then, rinse thoroughly with water. One application has been shown to protect more than 95% of patients against reinfestation for at least 2 weeks. In epidemic settings, a second prophylactic application is recommended 2 weeks after the first since the life cycle of a head louse is approximately 4 weeks.
Maximum Dosage Limits:
One application to affected area; do not repeat for >= 7 days.
Patients with Hepatic Impairment Dosing
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.
Patients with Renal Impairment Dosing
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.
*non-FDA-approved indication
There are no drug interactions associated with Permethrin products.
Permethrin is active against a broad range of pests, including lice, ticks, fleas, mites, and other arthropods. Permethrin acts on the nerve cell membrane to disrupt the sodium channel current that regulates the polarization of the membrane. This results in delayed repolarization and subsequent paralysis and death of the parasites. Permethrin exhibits residual ovicidal activity after rinsing.
Pharmacokinetics:
Permethrin is applied topically. The drug is rapidly metabolized by ester hydrolysis to inactive metabolites which are excreted primarily in urine.
-Route-Specific Pharmacokinetics
Topical Route
Although the amount of permethrin absorbed after a single application of 5% cream has not been precisely determined, data indicate that 2% or less of the amount of drug applied is absorbed in patients with moderate to severe scabies.