|Jmol 3D model||Interactive image|
|Molar mass||391.29 g·mol−1|
|Density||1.19 g/cm3, solid|
|Melting point||34 °C (93 °F; 307 K)|
|Boiling point||200 °C (392 °F; 473 K)|
|5.5 x 10−3 ppm|
|P03AC04 (WHO) QP53AC04 (WHO)|
|Main hazards||Irritating to skin and eyes,
damaging to lungs
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to rapidly harm most mammals or birds, but is toxic to fish and cats. In cats it may induce hyperexcitability, tremors, seizures, and death. In general, it has a low mammalian toxicity and is poorly absorbed by skin.
It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.
Permethrin is used:
- as an insecticide
- in agriculture, to protect crops (lethal for bees)
- in agriculture, to kill livestock parasites
- for industrial/domestic insect control
- in the textile industry to prevent insect attack of woollen products
- in aviation, the WHO, IHR and ICAO require arriving aircraft be disinsected prior to departure, descent or deplaning in certain countries
- to treat head lice in humans
- as an insect repellent or insect screen
- in timber treatment
- as a personal protective measure (cloth impregnant, used primarily for US military uniforms and mosquito nets)
- in pet flea preventative collars or treatment
- often in combination with piperonyl butoxide to enhance its effectiveness.
For treatment of scabies: Adults and children older than 2 months are instructed to apply the cream to the entire body from head to the soles of the feet. Wash off the cream after 8–14 hours. In general, one treatment is curative.
For treatment of head lice: Apply to hair, scalp, and neck after shampooing. Leave in for 10 minutes and rinse. Avoid contact with eyes.
In agriculture, permethrin is mainly used on cotton, wheat, maize, and alfalfa crops. Its use is controversial because, as a broad-spectrum chemical, it kills indiscriminately; as well as the intended pests, it can harm beneficial insects including honey bees, and aquatic life.
Permethrin kills ticks on contact with treated clothing. A method of reducing deer tick populations by treating rodent vectors involves stuffing biodegradable cardboard tubes with permethrin-treated cotton. Mice collect the cotton for lining their nests. Permethrin on the cotton instantly kills any immature ticks feeding on the mice.
Permethrin is used in tropical areas to prevent mosquito-borne disease such as dengue fever and malaria. Mosquito nets used to cover beds may be treated with a solution of permethrin. This increases the effectiveness of the bed net by killing parasitic insects before they are able to find gaps or holes in the net. Military personnel training in malaria-endemic areas may be instructed to treat their uniforms with permethrin, as well.
Permethrin is the most commonly used insecticide worldwide for the protection of wool from keratinophagous insects such as Tineola bisselliella.
Permethrin application can cause mild skin irritation and burning. Discontinue use if hypersensitivity occurs.
Permethrin has little systemic absorption, and is considered safe for topical use in adults and children over the age of 2 months. The FDA has assigned it as pregnancy category B. Animal studies have shown no effects on fertility or teratogenicity, but studies in humans have not been performed. The excretion of permethrin in breastmilk is unknown, and breastfeeding is recommended to be temporarily discontinued during treatment.
Absorption of topical permethrin is minimal. One in vivo study demonstrated 0.5% absorption in the first 48 hours based upon excretion of urinary metabolites.
Distribution of permethrin has been studied in rat models, with highest amounts accumulating in fat and the brain. This can be explained by the lipophilic nature of the permethrin molecule.
Metabolism of permethrin occurs mainly in the liver, where the molecule undergoes oxidation by the cytochrome P450 system, as well as hydrolysis, into metabolites. Elimination of these metabolites occurs via urinary excretion.
one cis enantiomer
Toxicology and safety
Permethrin acts as a neurotoxin, slowing down the nervous system through binding to sodium channels. This action is negatively correlated to temperature, thus, in general, showing more acute effects on cold-blooded animals (insects, fish, frogs, etc.) over warm-blooded animals (mammals and birds):
- Permethrin is extremely toxic to fish and aquatic life in general, so extreme care must be taken when using products containing permethrin near water sources.
- Permethrin is also highly toxic to cats, and flea and tick-repellent formulas intended and labeled for (the more resistant) dogs may contain permethrin and cause feline permethrin toxicosis in cats.
- Very high doses have tangible neurotoxic effects on mammals and birds, including human beings.
Permethrin is listed as a "restricted use" substance by the US Environmental Protection Agency (EPA) due to its high toxicity to aquatic organisms, so permethrin and permethrin-contaminated water should be properly disposed. Permethrin is quite stable, having a half life of 51–71 days in an aqueous environment exposed to light. It is also highly persistent in soil.
According to the Connecticut Department of Public Health, permethrin "has low mammalian toxicity, is poorly absorbed through the skin, and is rapidly inactivated by the body. Skin reactions have been uncommon."
Excessive exposure to permethrin can cause nausea, headache, muscle weakness, excessive salivation, shortness of breath, and seizures. Worker exposure to the chemical can be monitored by measurement of the urinary metabolites, while severe overdose may be confirmed by measurement of permethrin in serum or blood plasma.
Permethrin does not present any notable genotoxicity or immunotoxicity in humans and farm animals, but is classified by the EPA as a likely human carcinogen, based on reproducible studies in which mice fed permethrin developed liver and lung tumors. Carcinogenic action in nasal mucosal cells due to inhalation exposure is suspected, due to observed genotoxicity in human tissue samples, and in rat livers the evidence of increased preneoplastic lesions raises concern over oral exposure.
- 2002 study – "Our studies have documented low-dose effects of permethrin, doses below one-one thousandth of a lethal dose for a mouse, with effects on those brain pathways involved in Parkinson's disease [...] We have found effects consistent with a pre-parkinsonsian condition, but not yet full-blown parkinsonism." 
However, a 2007 study by the same researcher concluded "little hazard to humans" existed.
- 2007 study – "long-term, low-dose exposure to permethrin alone did not cause signs of neurotoxicity to striatal dopaminergic neural terminals, or enhance the effects of MPTP. We conclude that, under typical use conditions, permethrin poses little parkinsonian hazard to humans, including when impregnated into clothing for control of biting flies"
Pesticide-grade permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs having recently been treated with permethrin.
Toxic exposure of permethrin can cause several symptoms, including convulsion, hyperaesthesia, hyperthermia, hypersalivation, and loss of balance and coordination. Exposure to pyrethroid-derived drugs such as permethrin requires treatment by a veterinarian, otherwise the poisoning is often fatal. This intolerance is due to a defect in glucuronosyltransferase, a common detoxification enzyme in other mammals (that also makes the cat intolerant to paracetamol and many essential oils). The use of any external parasiticides based on permethrin is contraindicated for cats. (Cat ecotoxicology : cutaneous 100 mg/kg - oral 200 mg/kg.)[medical citation needed]
Permethrin was first synthesized in 1973. In general, the final step in the total synthesis of any of the synthetic pyrethroids is a coupling of a DV-acid ester and an alcohol. In the case of permethrin synthesis, the DV-acid cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, ethyl ester, is coupled with the alcohol, m-phenoxybenzyl alcohol, through a transesterification reaction with base. Tetraisopropyl titanate or sodium ethylate may be used as the base.
Numerous synthetic routes exist for the production of the DV-acid ester precursor. The pathway known as the Kuraray Process uses four steps. In general, the final step in the total synthesis of any of the synthetic pyrethroids is a coupling of a DV-acid ester and an alcohol. In the case of permethrin synthesis, the DV-acid cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, ethyl ester, is coupled with the alcohol, m-phenoxybenzyl alcohol, through a transesterification reaction with base. Tetraisopropyl titanate or sodium ethylate may be used as the base.
The alcohol precursor may be prepared in three steps. First, m-cresol, chlorobenzene, sodium hydroxide, potassium hydroxide, and copper chloride react to yield m-phenoxytoluene. Second, oxidation of m-phenoxytoluene over selenium dioxide provides m-phenoxybenzaldehyde. Third, a Cannizzaro reaction of the benzaldehyde in formaldehyde and potassium hydroxide affords the m-phenoxybenzyl alcohol.
It is marketed by Johnson & Johnson under the name Lyclear. In Nordic countries and North America, it is marketed under trade name Nix, often available over the counter.
- Stephen W. Page (2008). "10: Antiparasitic drugs". In Jill E. Maddison. Small Animal Clinical Pharmacology. Stephen W. Page, David Church. Elsevier Health Sciences. p. 236. ISBN 0-7020-2858-4. Retrieved 27 August 2014.
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- Insect-repelling ACUs now available to all Soldiers, United States Army, Canadian and
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- Permethrin chemical data