|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|
|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: / ?)(|
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. 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 dangerously toxic to fish and to cats: in cats it may induce hyperexcitability, tremors, seizures, and even death. In general, it has a low mammalian toxicity and is poorly absorbed by skin.
In medicine, permethrin is a first-line treatment for scabies; a 5% (w/w) cream 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.
It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.
- 1 Uses
- 2 Medical use
- 3 Pharmacokinetics
- 4 Military use
- 5 Stereochemistry
- 6 Toxicology and safety
- 7 See also
- 8 References
- 9 External links
Permethrin is used:
- as an insecticide
- in agriculture, to protect crops
- in agriculture, to kill livestock parasites
- for industrial/domestic insect control
- 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
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. It is important to put the tubes where mice will find them, such as in dense, dark brush, or at the base of a log; mice are unlikely to gather cotton from an open lawn.
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. An application should last several washes.
Permethrin is available for topical use as a cream or lotion. It is indicated for the treatment and prevention in exposed individuals of head lice (Pediculus humanus capitis) and treatment of scabies (Sarcoptes scabies). Permethrin formulations include a prescription-only 5% strength for scabies and an over-the-counter 1% strength for lice.
Dosage and administration
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.
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.
Permethrin is not tolerated in cats; It causes symptoms like convulsion, hyperaesthesia, hyperthermia, hypersalivation, loss of balance... These symptoms can be reversed with rapid and aggressive treatment by an experienced veterinarian, otherwise the poisoning is normally 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 with permethrin is contra-indicated for cats. (Cat ecotoxicology : cutaneous 100 mg·kg - Oral 200 mg·kg.)
- 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.
- "Permethrin". Pmep.cce.cornell.edu. 16 April 1986. Retrieved 5 January 2011.
- "WHO Model List of EssentialMedicines" (PDF). World Health Organization. October 2013. Retrieved 22 April 2014.
- R. H. Ian (1989). "Aquatic organisms and pyrethroids". Pesticide Science 27 (4): 429–457. doi:10.1002/ps.2780270408.
- "Permethrin (Lexi-Drugs)". Lexicomp Online. Wolters Kluwer. Retrieved 19 April 2014.
- "Permethrin Patient Package Insert" (PDF). FDA. Retrieved 19 April 2014.
- "Package Label" (PDF). Alpharma, USPD, Inc. Baltimore. Retrieved 19 April 2014.
- van der Rhee, HJ; Farquhar, JA; Vermeulen, NP (1989). "Efficacy and transdermal absorption of permethrin in scabies patients.". Acta dermato-venereologica 69 (2): 170–3. PMID 2564238.
- Tornero-Velez, R; Davis, J; Scollon, EJ; Starr, JM; Setzer, RW; Goldsmith, MR; Chang, DT; Xue, J; Zartarian, V; DeVito, MJ; Hughes, MF (Nov 2012). "A pharmacokinetic model of cis- and trans-permethrin disposition in rats and humans with aggregate exposure application.". Toxicological sciences : an official journal of the Society of Toxicology 130 (1): 33–47. doi:10.1093/toxsci/kfs236. PMID 22859315.
- Insect-repelling ACUs now available to all Soldiers, United States Army
- "report "Cats 'killed by flea treatment'"". BBC News. 10 November 2007. Retrieved 5 January 2011.
- Environmental Protection Agency. "Restricted Use Products (RUP) Report: Six Month Summary List". Retrieved 1 December 2009.
- Environmental Protection Agency. "Permethrin Facts (RED Fact Sheet)". Retrieved 2 September 2011.
- "Environmental Fate of Permethrin" (PDF).
- Kirby C. Stafford III (February 1999). "Tick Bite Prevention". Connecticut Department of Public Health.
- R. Baselt, Disposition of Toxic Drugs and Chemicals in Man, 8th edition, Biomedical Publications, Foster City, CA, 2008, pp. 1215–1216.
- Permethrin Facts, US EPA, June 2006.
- M. Tisch, P. Schmezer, M. Faulde, A. Groh and H. Maier (2002). "Genotoxicity studies on permethrin, DEET and diazinon in primary human nasal mucosal cells". European Archives of Oto-Rhino-Laryngology 259 (3): 150–153. doi:10.1007/s004050100406.
- K. Hakoi, R. Cabral, T. Hoshiya, R. Hasegawa, T. Shirai and N. Ito (1992). "Analysis of carcinogenic activity of some pesticides in a medium-term liver bioassay in the rat". Teratogenesis, Carcinogenesis, and Mutagenesis 12 (6): 269–276. doi:10.1002/tcm.1770120605.
- Bloomquist, J. R.; Barlow, R. L.; Gillette, J. S.; Li, W.; Kirby, M. L. (2002). "Selective effects of insecticides on nigrostriatal dopaminergic nerve pathways". Neurotoxicology 23 (4–5): 537–544. doi:10.1016/S0161-813X(02)00031-1. PMID 12428726.
-  BBC News, March 2006.
-  Virginia Tech, March 2003.
- Kou, J.; Bloomquist, J. R. (2007). "Neurotoxicity in murine striatal dopaminergic pathways following long-term application of low doses of permethrin and MPTP.". Toxicol Lett 171 (3): 154–161. doi:10.1016/j.toxlet.2007.05.005. PMID 17597311.
- Bouwman, H.; Sereda, B.; Meinhardt, H. M. (2006). "Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria-endemic area in South Africa". Environmental Pollution 144 (3): 902–917. doi:10.1016/j.envpol.2006.02.002. PMID 16564119.
- Linnett, P.-J. (2008). "Permethrin toxicosis in cats". Australian Veterinary Journal 86 (1–2): 32–35. doi:10.1111/j.1751-0813.2007.00198.x. PMID 18271821.
- Permethrin in the Pesticide Properties DataBase (PPDB)
- Permethrin Technical Fact Sheet – National Pesticide Information Center
- Permethrin General Fact Sheet – National Pesticide Information Center
- Permethrin-treated Clothing Hot Topic – National Pesticide Information Center
- "Health Effects of Permethrin-Impregnated Army Battle-Dress Uniforms", National Research Council (1994, US)
- "Permethrin summary report", Committee for Veterinary Products, European Agency for the Evaluation of Medical Products (1998, EU)
- Pesticide link to Parkinson Disease
- Permethrin Pesticide Information Profile – Extension Toxicology Network
- Permethrin chemical data