PERMETHRIN 1% MEDICATED SOAP

Indications

• Scabies
• Head lice
• Crab lice

Dosage

Children: For children, apply once weekly for 2 doses, applying preparation over the whole body including face, neck, scalp, and ears, and wash off after 8–12 hours.

Adults: Apply once weekly for 2 doses, applying 5% preparation over the whole body including the face, neck, scalp, and ears, and wash off after 8–12 hours.

Mechanism of action

Permethrin acts on the nerve cell membrane to disrupt the sodium channel current that regulates membrane polarization. This leads to delayed repolarization and paralysis of the pests. It is pediculocidal by interfering with sodium channel currents in the louse's nerve cell membranes, resulting in paralysis and death of the insect.

Pharmacodynamics

As a pyrethroid, permethrin is effective against a wide range of arthropods including lice, ticks, fleas, and mites. Its neurotoxic effects are due to its ability to prolong sodium channel activation, resulting in sustained depolarization of nerve membranes and subsequent paralysis of the parasites.

Pharmacokinetics

Permethrin is minimally absorbed through the skin, which limits systemic exposure. Its pharmacokinetics are influenced by the formulation used, but it is primarily localized to the application site. Metabolism occurs mainly in the liver, and it is eliminated through fecal and urinary routes.

Contra-indications

• Hypersensitivity to permethrin or any of its excipients
• Children under 6 months (for certain formulations without medical supervision)
• Broken or secondarily infected skin

Adverse effects

• Scalp irritation
• Skin reactions
• Burning sensation
• Contact dermatitis
• Allergic reactions

Precautions

• Avoid contact with eyes
• Avoid contact with mucous membranes
• Medical supervision required for children under 2 years
• Caution in patients with severe eczema or asthma

Pregnancy

Permethrin should be used during pregnancy only if clearly needed and if the benefits outweigh the risks.

Breast-feeding

Permethrin is generally considered safe during breastfeeding, but caution should be exercised.

Storage

Store in a cool, dry place, away from direct sunlight.

Formulations

• 5% cream
• Cutaneous spray solution
• Lotion
• Other topical formulations

Mechanism of action

Permethrin acts on the nerve cell membrane to disrupt the sodium channel current by which the polarization of the membrane is regulated. Delayed repolarization and paralysis of the pests are the consequences of this disturbance. Permethrin is pediculocidal by disrupting in sodium channel current in the louse's nerve cell membrane; this action causes delayed polarization of the membrane and paralysis of the insect. Like natural pyrethrins, permethrin acts as a neurotoxin by depolarizing nerve cell membranes of parasites. The drug disrupts the sodium channel current by which membrane repolarization is regulated. Delayed repolarization results in paralysis of the nerves in the exoskeletal respiratory muscles of the parasite leading to death. The synthetic pyrethroids delay closure of the sodium channel, resulting in a sodium tail current that is characterized by a slow influx of sodium during the end of depolarization. Apparently the pyrethroid molecule holds the activation gate in the open position. Pyrethroids with an alpha-cyano group (e.g., fenvalerate) produce more prolonged sodium tail currents than do other pyrethroids (e.g., permethrin, bioresmethrin). The former group of pyrethroids causes more cutaneous sensations than the latter. /Synthetic pyrethroids/ Trans- and cis-permethrin were irradiated in sunlight and at gamma>290 nm in hexane, methanol, water and water acetone. Isomerization and ester cleavage occurred primarily. Observed products included monochloropermethrin and the monochlorovinyl acid from cleavage, 3-phenoxybenzyl 3,3-dimethylacrylate, 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, benzyl alcohol, benzaldehyde, 3-hydroxybenzyl alcohol, benzoic acid, 3-hydroxybenzoic acid, and 3-phenoxybenzyl alcohol. For more Mechanism of Action (Complete) data for PERMETHRIN (10 total), please visit the HSDB record page.

Pharmacodynamics

Permethrin, a pyrethroid, is active against a broad range of pests including lice, ticks, fleas, mites, and other arthropods.