Permethrin LMP (50 mg/g Gel)

What Is Permethrin LMP and What Is It Used For?

Permethrin LMP is a prescription-only topical gel containing 50 mg/g (5%) of permethrin, a synthetic pyrethroid insecticide. It is used to kill mites and lice that cause skin infestations — most importantly scabies (Sarcoptes scabiei) and pediculosis (lice). Permethrin is considered the reference treatment for scabies in most international clinical guidelines.

Permethrin is a member of the pyrethroid family of synthetic insecticides, developed in the 1970s as stable analogues of pyrethrins derived from Chrysanthemum cinerariifolium. It is included on the WHO Model List of Essential Medicines because of its high efficacy, favourable safety profile, and low cost. The LMP formulation is a 5% topical gel (50 mg of permethrin per gram of gel base), designed for cutaneous application to the affected skin.

The principal clinical indication is the treatment of classic (typical) scabies, a highly contagious skin infestation caused by the female mite Sarcoptes scabiei var. hominis. The mite burrows into the upper layer of the epidermis, where it lays eggs, triggering an intensely itchy hypersensitivity response that typically worsens at night. Scabies affects an estimated 200–300 million people globally each year and is a WHO-recognised neglected tropical disease. Permethrin 5% is also used off-label or by prescription against Pthirus pubis (pubic lice / “crabs”) and sometimes Pediculus humanus capitis (head lice), although dedicated lice formulations at 1% permethrin are more commonly used for head lice.

Mechanism of action: Permethrin binds to voltage-gated sodium channels in the nervous system of arthropods and delays their closure. This prolongs the flow of sodium into nerve cells, causing repetitive firing, paralysis, and death of the mite or louse. Mammalian sodium channels are much less sensitive to pyrethroids, and human skin, liver, and plasma esterases rapidly hydrolyse permethrin into inactive metabolites. The combination of selective arthropod toxicity, poor skin penetration, and rapid mammalian metabolism explains the wide therapeutic window of topical permethrin.

Permethrin 5% gel is effective against all life stages of S. scabiei, including eggs, larvae, nymphs, and adult mites. Clinical trials and Cochrane systematic reviews have consistently demonstrated cure rates of 89–98% after a single or repeat application, making it comparable to or more effective than oral ivermectin, benzyl benzoate, and malathion in most settings.

What Should You Know Before Using Permethrin LMP?

Before using Permethrin LMP, tell your doctor about any known allergies (especially to chrysanthemum, pyrethroids or pyrethrins), about pregnancy or breastfeeding, and about any skin conditions. The gel is for external use only and must be applied to clean, cool, dry, undamaged skin.

Permethrin LMP has a very favourable safety profile when used as directed, but a careful assessment by a healthcare professional is still required to confirm the diagnosis and exclude contraindications. The diagnosis of scabies is often based on clinical features (intense nocturnal itching, characteristic distribution of burrows in the finger webs, wrists, axillae, genital region, and waistline) and can be confirmed by dermoscopy or microscopic examination of skin scrapings.

Inform your doctor or pharmacist if you have any of the following before using Permethrin LMP: a known allergy to permethrin, any other pyrethroid, pyrethrin, or chrysanthemum-derived product; extensive skin disease (eczema, psoriasis, infected dermatitis); broken, weeping or severely inflamed skin; a history of asthma that has worsened with exposure to pyrethroids; hepatic impairment; or any suspicion of infection with crusted (Norwegian) scabies, which requires more intensive treatment.

Contraindications

Permethrin LMP should not be used in the following situations:

• Known hypersensitivity to permethrin, other pyrethroids, pyrethrins, chrysanthemums, or any excipient in the gel formulation.
• Infants under two months of age unless specifically prescribed and supervised by a paediatric dermatologist; the skin barrier function is immature and systemic absorption may be higher.
• Application to the eyes, mouth, or other mucous membranes. If accidental contact occurs, rinse thoroughly with water and seek medical advice if irritation persists.
• Open wounds, active infections, or severely inflamed skin, where absorption is increased and the gel may cause stinging, burning, and delayed healing.

People with a documented systemic hypersensitivity reaction to permethrin (e.g., urticaria, angioedema, or anaphylaxis) must not use this product. Because of rare but reported cross-reactivity, caution is advised in individuals with known allergy to any member of the pyrethroid/pyrethrin family. If you are uncertain about your allergy history, ask your doctor to perform a careful review before prescribing.

Warnings and Precautions

Talk to your doctor before using Permethrin LMP if any of the following apply:

• Asthma or reactive airway disease: Pyrethroids can occasionally trigger bronchospasm in sensitive patients. Avoid inhalation and apply in a ventilated room.
• Eczema, psoriasis or other inflammatory skin disease: The gel may cause more stinging and irritation on damaged skin and may require an alternative product.
• Crusted (Norwegian) scabies: Hyperkeratotic forms of scabies harbour millions of mites and require a combined regimen of topical permethrin and oral ivermectin under specialist supervision.
• Liver impairment: Although systemic absorption is low, permethrin is metabolized by hepatic esterases; severe impairment may theoretically slow its clearance.
• Recent use of topical corticosteroids: These can mask the clinical features of scabies and may require a steroid-free interval before diagnosis.

During application, avoid contact with the eyes, inside of the mouth, inside of the nose, and genital mucosa. If you wash your hands or any part of the body during the 8–12 hour treatment period, reapply the gel to that area afterwards to maintain continuous contact. Apply to cool, dry skin; hot, damp skin and recent bathing in hot water can increase vasodilation and systemic absorption.

Re-infestation is a common reason for apparent “treatment failure”. Because scabies mites can survive up to 36–72 hours away from a human host, all clothing, bedding, towels, and other soft articles used in the three days before treatment should be washed at 60°C (140°F) or higher, tumble-dried on hot, dry-cleaned, or sealed in a plastic bag for at least 72 hours. All close contacts — household members, sexual partners, carers — should be treated simultaneously, regardless of whether they have symptoms.

Pregnancy and Breastfeeding

Topical permethrin is one of the most extensively studied scabicides in pregnancy and is considered compatible with pregnancy by the WHO, CDC, and the UK Teratology Information Service. Systemic absorption after cutaneous application is very low (typically <2%), animal reproduction studies have not shown teratogenicity at exposures relevant to topical use, and no increase in adverse pregnancy outcomes has been observed in human studies. For this reason, topical 5% permethrin is generally preferred over oral alternatives (such as ivermectin) during pregnancy when treatment is required.

If you are pregnant, think you may be pregnant, or are planning to become pregnant, inform your doctor before starting Permethrin LMP so that the potential benefits and risks can be individually assessed. Untreated scabies during pregnancy can spread within the household and increases the risk of secondary bacterial skin infection, so timely treatment is usually advised when indicated.

During breastfeeding, topical permethrin can generally be used if clinically indicated. Because the molecule is poorly absorbed through intact skin and is rapidly metabolized, negligible amounts are expected to reach breast milk. To minimise infant exposure, avoid applying the gel directly to the nipple and areola just before feeding; if application to that area is necessary, wipe the region clean with a damp cloth before the baby feeds, or briefly pause breastfeeding during the 8–12 hour treatment window and express milk.

How Does Permethrin LMP Interact with Other Drugs?

Because Permethrin LMP is applied topically and has very low systemic absorption, clinically significant systemic drug interactions are rare. Most interactions involve other topical products applied to the same skin area or products that alter the skin barrier.

Drug interactions with topical permethrin fall into two main categories: pharmaceutical/local interactions, which occur on the skin surface or within the skin, and theoretical pharmacokinetic interactions, which may occur when systemic absorption is increased (for example by damaged skin or excessive application). In clinical practice, systemic interactions are uncommon, but prescribers routinely take a full medication history to avoid overlap with other antiparasitic drugs, immunosuppressants, or irritants.

When both permethrin and another topical product are prescribed simultaneously, care should be taken to avoid applying them to the same area at the same time. For example, topical corticosteroids may dampen the inflammatory signs of scabies, masking the clinical picture and delaying diagnosis; they should generally be stopped in the treated area for several days before starting permethrin unless specifically directed by a dermatologist. Emollients and moisturisers can be used before or after permethrin treatment but should not be applied in the 8–12 hours that the gel is in contact with the skin.

Patients using oral antiparasitic agents (such as ivermectin for crusted scabies) alongside Permethrin LMP should do so under specialist supervision. This combination is recommended for hyperkeratotic or treatment-resistant forms of scabies; when used together, both medicines are generally well tolerated, but dosing schedules need to be coordinated to maximise efficacy and minimise adverse effects.

Potential Drug Interactions

This table is not exhaustive. Always bring a complete, up-to-date list of your medicines, including over-the-counter products, dietary supplements, topical preparations, and herbal remedies, to any medical consultation. Your pharmacist can screen for potential interactions and help you plan the timing and sequencing of applications.

What Is the Correct Dosage of Permethrin LMP?

For adult scabies treatment, apply one thin layer of Permethrin LMP 5% gel to the entire body from the neck down, leave it in place for 8–12 hours (usually overnight), then wash off thoroughly. A typical adult requires 30–60 g per application. A second treatment 7–14 days later is often recommended. Always follow the specific instructions given by your doctor or pharmacist.

The correct dosage and duration of Permethrin LMP depend on the indication (scabies versus pediculosis), the patient's age, body surface area, the presence of crusted or hyperkeratotic lesions, and previous treatment response. Dosing is based on complete coverage of the affected skin rather than on body weight. The quantity of gel required increases with body size, from approximately 3–5 g for a newborn to 60 g or more for a large adult.

Adults and Adolescents (≥12 years)

Infants, Children and Adolescents

Elderly Patients

Missed Dose

Because Permethrin LMP is not a daily medication, “missing a dose” in the traditional sense is unusual. If you forget to apply the gel on the planned treatment evening, apply it as soon as possible, ideally in the evening so that the 8–12 hour contact period occurs overnight. If a recommended second application (7–14 days after the first) is missed, apply it as soon as you remember; do not apply it twice on the same day.

If you wash off the gel earlier than 8 hours after application, reapply a fresh layer and resume the contact period. Insufficient contact time is one of the most frequent causes of apparent treatment failure.

Overdose

What Are the Side Effects of Permethrin LMP?

The most frequent side effects of Permethrin LMP are mild, short-lasting, and confined to the skin. They include tingling, burning, itching, and redness at the application site. Serious systemic or allergic reactions are rare. Contact your doctor if symptoms are severe, persistent, or spreading.

Side effects of medicines are usually classified by frequency: very common (>1 in 10 people), common (1 in 10 to 1 in 100), uncommon (1 in 100 to 1 in 1,000), rare (1 in 1,000 to 1 in 10,000), and very rare (<1 in 10,000). The side-effect profile of topical permethrin is dominated by local skin reactions; systemic side effects are uncommon because of the very limited absorption of the active substance.

It is important to distinguish side effects caused by the medication from post-scabetic pruritus, the residual itching that remains for 2–4 weeks after successful scabies treatment. This is an allergic response to antigens left behind by the dead mites, not a sign of treatment failure. Moisturisers, oral antihistamines (such as cetirizine or loratadine), and, in some cases, short courses of topical corticosteroids prescribed by a doctor can relieve this itching. New burrows, vesicles, or fresh papules appearing more than four weeks after treatment warrant re-evaluation for re-infestation or treatment resistance.

Most cutaneous side effects of permethrin are dose-dependent and self-limiting. They are typically more pronounced in people with pre-existing skin disease (eczema, psoriasis), very dry skin, or when the gel has been left on under occlusion (plastic film, tight clothing). Reducing occlusion, applying emollients before and after treatment, and ensuring that the skin is cool and dry at the moment of application can reduce the likelihood and severity of local reactions.

Serious hypersensitivity reactions, including urticaria, angioedema, and anaphylaxis, are rare but have been reported. Any patient who develops swelling of the face, lips, tongue, or throat, difficulty breathing, or a rapidly spreading rash during or after application should stop treatment immediately and seek emergency medical care.

You are encouraged to report any suspected adverse reactions to your healthcare provider or to your national pharmacovigilance authority. Reporting helps regulatory agencies identify previously unknown adverse events and improves safety information for all patients.

How Should You Store Permethrin LMP?

Store Permethrin LMP gel at room temperature below 25°C (77°F) in its original tube and packaging. Do not freeze. Keep out of reach and sight of children. Do not use after the expiry date printed on the carton.

Correct storage of Permethrin LMP is important to preserve its quality, safety, and effectiveness. The gel should be kept in a cool, dry place at a temperature not exceeding 25°C (77°F). Avoid direct sunlight, high humidity, and heat sources such as radiators or cookers. The tube must remain tightly closed between uses. Do not freeze the product; freezing can damage the gel matrix, alter its consistency, and affect drug distribution.

Keep the product in its original packaging until use. The tube and carton are designed to protect the active substance from light, which can degrade pyrethroids. Check the appearance of the gel before application: it should be a homogeneous, smooth preparation without separation or discoloration. If the gel has changed colour, become lumpy, or smells unusual, do not use it and return the product to your pharmacist.

Always keep Permethrin LMP and all medicines out of the reach and sight of children. Accidental ingestion of a pyrethroid gel by a child is a medical incident that requires prompt attention. Store the tube in a locked medicine cabinet whenever possible and never transfer the gel to another container.

Do not use Permethrin LMP after the expiry date stated on the packaging. The expiry date refers to the last day of the indicated month. Expired medicines may have reduced potency and could cause unintended skin reactions. Once a tube has been opened, follow any shelf-life information provided in the patient information leaflet regarding use within a specific period after first opening.

What Does Permethrin LMP Contain?

Each gram of Permethrin LMP gel contains 50 mg (5%) of the active substance permethrin, together with a range of inactive excipients that form the gel base, preserve the product, and improve its cosmetic properties on the skin.

The active ingredient in Permethrin LMP is permethrin 50 mg per gram of gel (5% w/w). Permethrin is a 1:3 mixture of the cis and trans isomers of a synthetic pyrethroid. Its chemical name is (3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane-1-carboxylate, and it has the CAS number 52645-53-1. Permethrin is practically insoluble in water but soluble in many organic solvents; this physicochemical profile is compatible with oil-in-water and alcohol-based gel formulations.

The inactive ingredients (excipients) in a typical permethrin 5% gel formulation may include gelling agents (for example carbomer or hydroxypropyl methylcellulose), solvents (isopropyl alcohol, propylene glycol), emulsifiers, surfactants, pH-adjusting agents, and purified water. The gel base is designed to spread easily over the skin, dry quickly without leaving a sticky residue, and maintain intimate contact with the skin surface for the 8–12 hour treatment period. The precise list of excipients is stated in the patient information leaflet included in the pack; consult this leaflet if you have known intolerances (for example, propylene glycol sensitivity).

People who are allergic to any of the excipients or to pyrethroids as a class should not use this product. If you have a history of contact dermatitis to cosmetics, hair products, or insecticides containing pyrethroids, inform your doctor before starting Permethrin LMP. In most patients, however, the formulation is well tolerated on healthy skin.

Permethrin LMP is supplied in aluminium tubes sealed with a screw cap and containing a weight of gel appropriate for one or more treatment courses. Always check the packaging before use to confirm that it is intact and that the batch number and expiry date are clearly legible.

Frequently Asked Questions About Permethrin LMP