Permethrin

Permethrin: Comprehensive Patient Information

Basic Product Information

Mechanism of Action

For patients: Permethrin belongs to a group of medicines called synthetic pyrethroids and works by paralysing and killing mites (such as scabies) and lice. It targets their nervous system by blocking normal nerve function, which results in their death.

For specialists: Permethrin acts on sodium channels of nerve cell membranes of parasites, prolonging channel activation and causing repetitive nerve impulses, paralysis, and death. It selectively affects arthropod sodium channels, sparing mammals at recommended doses.

Pharmacokinetics

• Absorption: Less than 2% of topically applied permethrin is absorbed through intact human skin.
• Metabolism: Systemically absorbed permethrin is rapidly metabolised in the liver via ester hydrolysis.
• Elimination: Permethrin metabolites are principally excreted in urine within days.
• Duration of Action: One topical application remains effective for up to 7–14 days.

Use in Everyday Life and Best Practices

Permethrin is widely used in Australia for treating head lice and scabies infestations. It is simple to apply but following the correct protocol is essential to ensure effectiveness and prevent reinfestation. Most commonly, products are available as lotions (for lice) or creams (for scabies).

• For scabies (cream): Apply the 5% cream to clean, dry skin as a thin layer over the entire body from the chin down (including under nails and skin folds), leave on for 8–14 hours (usually overnight), then wash off.
• For head lice (lotion or shampoo): Apply 1% lotion/shampoo to dry hair and scalp, leave on for 10 minutes, then wash with regular shampoo and comb through with a fine-tooth comb to remove dead lice and nits.
• Re-treatment is usually recommended after 7 days to kill any newly hatched lice or mites.
• Family members or close contacts may also require simultaneous treatment.
• Bedding, clothing, and towels should be washed in hot water and dried thoroughly to prevent reinfestation.

Dosing in the Morning vs Evening

Scabies treatment: Evening application is preferred, as the cream needs to remain on the skin for 8–14 hours, optimally overnight while you sleep. This minimises disruption to daily activities and maximises efficacy. Morning application is possible but may require planning to keep skin covered and avoid washing.

Head Lice treatment: Timing is less critical, but many patients find evening application convenient to coordinate with home routines. Regularity—particularly if a second treatment is needed—is more important than the specific time of day.

Taking with Food or on an Empty Stomach

Permethrin is for external use only (not to be ingested). Food or meal timing does not affect absorption or efficacy. There are no known interactions with typical Australian diets, and no dietary restrictions apply.

Interaction Warnings

Indications

Dosing According to Clinical Indications

Safety Profile and Side Effects

• Common: Mild itching, stinging, redness, burning, or tingling at site of application; temporary worsening of skin irritation (especially if severe infestation).
• Rare: Allergic skin reactions (rash, swelling), contact dermatitis, numbness or tingling, systemic allergic reactions (extremely rare).
• Warnings:
  • Avoid contact with eyes, mouth, and mucous membranes; rinse thoroughly with water if accidental exposure occurs.
  • Do not apply to broken or inflamed skin unless advised by a healthcare professional.
  • Consult a doctor before use in younger infants or patients with chronic skin conditions.

Guidelines for Proper Use

1. Always read the package leaflet before use and follow your pharmacist’s advice.
2. Apply product to cool, dry skin (not immediately after hot showers/baths) to reduce irritation.
3. For head lice, comb hair first to remove tangles, ensuring even coverage.
4. Wash clothing, bedding, and towels at >60°C or dry clean to destroy eggs/mites/lice.
5. Reapply as directed—usually after 7 days—to ensure eradication of eggs.
6. Do not share combs, hats, or personal items during treatment.
7. Family members in close contact should be treated at the same time to prevent reinfection.
8. Store product below 30°C and out of reach of children.

Alternative Treatment Options

• Benzyl Benzoate: Often used for scabies, but generally less well-tolerated than permethrin (causes more skin irritation).
• Malathion: Used for head lice; available as a lotion, second-line due to odour and risk of irritation.
• Ivermectin (oral or topical): Reserved for resistant cases or when topical treatments fail; requires medical prescription.
• Wet-combing: Non-chemical method for head lice; less effective but may be preferred in young children or in case of resistance/intolerance.
• Tea tree oil and other natural remedies: Not routinely recommended due to lack of robust evidence and possible skin irritation.

Permethrin is generally the first-line, best-tolerated, and most effective option for both scabies and head lice in Australia. Other alternatives are used in cases of intolerance, side effects, or drug resistance.

Legal, Registration, and Reimbursement Status in Australia

• Registered with the Therapeutic Goods Administration (TGA) for use in scabies and head lice.
• Schedule 2 (Pharmacy Medicine): Available without doctor’s prescription but restricted to sale in pharmacies only.
• Select formulations may be subsidised for specific indications/at-risk groups via the Pharmaceutical Benefits Scheme (PBS).
• No special reimbursement required for most uses, but patients with persistent infestations may require a doctor’s review and prescription.

Latest Research and Clinical Guidance (2022–2025)

Recent Australian and international guidelines—including those from the Australian Society for Infectious Diseases (ASID) and UK NICE—continue to support 5% permethrin as the first-line treatment for scabies and 1% formulations for head lice. Resistance remains low in Australia, but increasing cases of global resistance highlight the importance of strict adherence to treatment protocols and simultaneous management of contacts (Nair PA, Singhal R, 2023; Chosidow O, 2024). A review by the Therapeutic Guidelines Australia (2024) confirms permethrin’s ongoing efficacy, and research into combination therapies (permethrin + oral ivermectin) is ongoing for severe or crusted scabies, especially in high-risk settings.

Availability and Delivery

*Delivery times are estimates for online pharmacy orders; availability may vary by local stock. Always check expiry date and product seal before use.

Frequently Asked Questions (FAQs)

1. Can I use permethrin if I am pregnant or breastfeeding?
   Permethrin cream is not absorbed significantly through the skin and is considered safe for use in pregnancy and while breastfeeding. However, discuss with your doctor or pharmacist before use.
2. How soon after treatment will itching stop?
   Itching may persist for up to 2 weeks after successful treatment due to ongoing skin irritation and immune response, not because of ongoing infestation. If symptoms persist beyond 3–4 weeks, consult your doctor.
3. What if I accidentally get permethrin in my eyes or mouth?
   Rinse thoroughly with clean water for at least 10 minutes. Seek medical attention if irritation continues, especially with eye exposure.
4. Do I need to treat the whole household?
   Yes—for scabies, all close contacts should be treated at the same time, even if they do not have symptoms. For head lice, treat anyone with confirmed infestation and check all family members.
5. Can permethrin be used for pets?
   Some veterinary formulations exist, but never use human permethrin for pets—accidental overdoses can be dangerous, especially in cats. Consult your veterinarian.