What it's for (Indications)
- Permethrin, a synthetic pyrethroid, is broadly indicated for the topical treatment of two significant parasitic infestations: scabies (Sarcoptes scabiei) and pediculosis (infestation with head lice, Pediculus humanus capitis).
- For scabies, a 5% cream formulation (e.
- g.
- , Lotrix Cream) is typically prescribed, applied as a single treatment to the entire body surface from the neck down, including areas between fingers and toes, and under nails.
- This application is highly effective in eradicating the mites responsible for scabies.
- For pediculosis, a 1% lotion or cream rinse is utilized, applied to the hair and scalp to kill live lice and their nits (eggs).
- Its efficacy against both adult parasites and their eggs makes permethrin a first-line agent in the management of these common dermatological conditions, providing significant relief from pruritus and preventing further transmission.
- The exact formulation and concentration depend on the specific indication.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | The dosage and application methodology for permethrin are specific to the condition being treated and the formulation used. For scabies, using the 5% cream (such as Lotrix Cream), adults and children aged 2 months and older should apply a thin layer to the entire skin surface from the neck down, including soles of the feet, spaces between fingers and toes, and under fingernails. For infants and the elderly, the scalp, temples, and forehead should also be treated. The cream must remain on the skin for 8 to 14 hours before being thoroughly washed off with water. A single application is usually curative, but a second application 7 to 14 days later may be considered if live mites are still present or new lesions appear. For head lice, a 1% lotion or cream rinse is applied to shampooed, towel-dried hair, saturating the hair and scalp. It should be left on for 10 minutes and then thoroughly rinsed with water. Combing with a fine-toothed nit comb is recommended to remove dead lice and nits. A second application for head lice is generally advised 7 to 10 days after the initial treatment to eliminate newly hatched lice from surviving nits. |
Safety & Warnings
Common Side Effects
- Permethrin is generally well-tolerated, but localized cutaneous adverse reactions are the most common side effects observed.
- These typically include transient and mild sensations at the application site such as itching (pruritus), burning, stinging, tingling, numbness, erythema (redness), and dry skin.
- The itching associated with scabies may paradoxically persist or even intensify for up to several weeks following successful treatment, often due to an ongoing allergic reaction to dead mites and their debris, rather than indicating treatment failure or re-infestation.
- Patients should be counselled about this post-scabies pruritus.
- Less commonly, patients may experience mild skin rash, edema, or discomfort.
- Systemic absorption of permethrin through topical application is minimal, thereby significantly limiting the potential for systemic adverse effects.
- Patients should be advised to contact a healthcare professional if these symptoms become severe, persistent, or if signs of an allergic reaction develop.
Serious Warnings
- Black Box Warning: Serious Warnings: Permethrin, while generally safe for topical use, carries important warnings that warrant careful attention. It is intended solely for external dermatological application and must never be ingested due to the potential for systemic toxicity, though severe effects from accidental oral exposure are rare given its poor gastrointestinal absorption. Strict precautions must be observed to prevent contact with the eyes, mouth, nose, and other mucous membranes. Should accidental contact occur, immediately and thoroughly flush the affected area with copious amounts of water. Application to compromised skin, such as open wounds, severely inflamed, or extensively excoriated areas, should be avoided as it may lead to increased systemic absorption, potentially escalating the risk of systemic adverse effects. Patients should be educated that persistent pruritus (itching) following successful scabies treatment often represents a post-scabies allergic reaction to dead mites and does not necessarily indicate treatment failure or re-infestation; re-treatment should only proceed after re-evaluation by a healthcare professional and confirmed presence of live parasites. For infants younger than 2 months (scabies) or 2 years (head lice), use requires careful medical consideration due to insufficient safety data.
- Permethrin is strictly for external dermatological use and must not be ingested.
- Extreme caution must be exercised to prevent contact with eyes and mucous membranes, including the mouth, nose, and genital area.
- In the event of accidental ocular contact, the eyes should be immediately and thoroughly flushed with copious amounts of water.
- Patients with known hypersensitivity or allergic reactions to permethrin, other synthetic pyrethroids, pyrethrins, or any component of the formulation should avoid its use.
- Discontinue treatment if severe irritation, sensitization, or allergic reaction develops.
- Application to open wounds, inflamed, or severely excoriated skin should be avoided, as this may potentially increase systemic absorption.
- While systemic absorption is low, pregnant or breastfeeding individuals should use permethrin only if clearly indicated and after careful consideration of potential risks versus benefits, following consultation with a healthcare provider.
- Safety in infants younger than 2 months for scabies and younger than 2 years for head lice has not been definitively established, and medical consultation is imperative before use in these age groups.
- Keep permethrin out of reach of children.
How it Works (Mechanism of Action)
Permethrin is a synthetic pyrethroid, belonging to a class of neurotoxic insecticides chemically related to the natural pyrethrins derived from chrysanthemum flowers. Its mechanism of action involves disrupting the normal physiological function of the nerve cells in parasites, specifically targeting voltage-gated sodium channels. Permethrin binds to these channels in the nerve cell membranes of arthropods (mites and lice), causing a prolonged depolarization. This leads to repetitive discharges, hyperexcitability, and ultimately results in central nervous system paralysis, respiratory failure, and death of the parasite. This neurotoxic effect is highly selective for invertebrates, due to structural differences in their sodium channels and lower metabolic detoxification capacity compared to mammals, explaining its relatively high safety profile in humans when applied topically. Furthermore, permethrin exhibits ovicidal activity, effectively killing the eggs (nits) of lice, contributing to its high efficacy in eradicating infestations.
Commercial Brands (Alternatives)
No other brands found for this formula.