Permethrin is an antiparasitic active ingredient used in veterinary and human medicine, It is used in livestock and pets against external parasites (lice, mites, fleas, fliesticks, etc.). It is also used against agricultural and household pests. It belongs to the chemical class of the synthetic pyrethroids.

Common name: PERMETHRIN

Type: pesticide
Chemical class: synthetic pyrethroid


Molecular structure of PERMETHRIN





Type of action: Broad spectrum contact, non systemic ectoparasiticide: insecticide, acaricide, tickicide, louisicide, larvicide
Main veterinary parasites controlled: flies, ticks, mites, lice, fleas, mosquitoes, etc.

Efficacy against a specific parasite depends on the delivery form and on the dose administered. 

Click here for general information on features and characteristics of PARASITICIDES.


Click here to view the article in this site with the most common dosing recommendations for permethrin used in domestic animals.


Oral LD50, rat, acute*:  430-4000 mg/kg depending on vehicle and content of various isomers
Dermal LD50, rat, acute*: >4000 mg/kg
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.

WARNING: Permethrin is toxic for cats!

Synthetic pyrethroids can be irritant for the skin and the eyes.

MRL (maximum residue limit) set for animal tissues (either beef, mutton pork or chicken)*:

  • CODEX: Yes
  • EU: Yes
  • USA: Yes
  • AUS: Yes

* This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock. MRL's for animal tissues may be set also for agricultural pesticides that are not approved for use on animals but are used on commodities fed to animals. A MRL may be also set in the form of an IMPORT TOLERANCE for active ingredients not approved in a particular country but approved for imported animal commodities.

Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.

Learn more about permethrin safety.

General information on the safety of veterinary antiparasitics is available in specific articles in this site (click to visit):


Never use agricultural or hygiene products with this or any other active ingredient on livestock or pets, even if there are veterinary products with this same active ingredient approved for use on animals. The formulations for agricultural or hygiene use are different and may be toxic for livestock or pets.

It is obvious that veterinary products are not intended for and should never be used on humans!!!


Decade of introduction: 1970
Introduced by: FMC, ICI, SHELL, SUMITOMO, etc.
Some original brands: ECTIBAN, STOMOXIN
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, moderate.
Use in HORSES. Yes, abundant.
Use in
DOGS: Yes, massive.
Main delivery forms: 

Use in human medicine: Yes
Use in
public/domestic hygiene: Yes
Use in
agriculture: Yes
Generics available: 
Yes, numberless



Visit also the section in this site about parasite resistance to antiparasitics and more specifically to permethrin.


Permethrin is a synthetic pyrethroid with a spectrum of activity similar to cypermethrin. It is massively used in dogs, substantially less in livestock. It is also vastly used in agriculture, as well as in public and domestic hygiene. Together with cypermethrin it is one of the synthetic pyrethroids most used worldwide.

There are also many mixtures: with amitraz, organophosphates, carbamates, insect development inhibitors, etc. Many products contain also synergists.

Permethrin used in veterinary products can be of different "qualities" regarding the content of various optic isomers (cis or trans) that show different efficacy against parasites. You can learn more about such mixtures of optic isomers in the article on synthetic pyrethroids. For most users, it often doesn't make any difference regarding efficacy, because if one product uses a mixture with more of the most effective isomers, it will be used at a lower concentration than a product using a mixture with less effective isomers. However, some isomers are significantly more toxic than other ones, and this can negatively influence the tolerance of livestock or pets to a particular product.

Efficacy of permethrin

Permethrin is an ectoparasiticide, i.e. active only against external parasites such as flies, ticks, mites, lice, fleas, mosquitoes, etc. It can be considered as a broad-spectrum generalist, i.e. quite good against almost all insects, ticks and mites, but not outstanding against a particular parasite. It is certainly less efficient against multi-host ticks (e.g. Amblyomma, Rhipicephalus, Ixodes, Dermacentor, etc.) than several other tickicides (e.g. amitraz, chlorfenvinphos, coumaphos, flumethrin, etc.).

As most synthetic pyrethroids, permethrin is a mediocre larvicide, i.e. it is often not a good option for the large-scale prevention of cutaneous myiases (e.g. screwworms, blowfly strike, etc.) with sprays, pour-ons, etc. However permethrin is often included in dressings for the therapeutic treatment on animal injuries already infected with maggots.

Permethrin, as well as many other synthetic pyrethroids has a significant repellent effect on certain insects and ticks, which strongly depends on the delivery form and the dose administered.

However, resistance to permethrin is widespread and can be very high in cattle ticks (Boophilus spp), horn flies (Haematobia irritans), red poultry mites (Dermanyssus gallinae), sheep lice (Damalinia ovis), houseflies (Musca domestica), dog and cat fleas (Ctenocephalides spp) and mosquitoes. As a consequence, products with permethrin are already totally useless against these important parasites in many places. The same applies to all other synthetic pyrethroids (e.g. cypermethrin, deltamethrin, flumethrin, etc.). And this is true for whatever delivery form: dipping, spraying, pour-ons, ear-tags, shampoos, soaps, etc.

Pharmacokinetics of permethrin

Topically administered permethrin remains mostly on the hair-coat of the treated animals and is very poorly absorbed through the skin. In contrast with natural pyrethrins and older synthetic pyrethroids permethrin is quite resistant to UV-light, which allows a residual effect between 5 and 10 days for most sprays and dips.

Treated animals can ingest permethrin through licking or grooming. Absorption to blood is low. The absorbed permethrin is quickly metabolized in the liver to non-toxic metabolites that are excreted through urine. This is done by a specific enzyme called glucuronidase. However, cats lack this enzyme and cannot metabolize permethrin and other synthetic pyrethroids. This is why permethrin and most other synthetic pyrethroids are toxic to cats.

As a general rule permethrin products are approved for use on dairy animals and on laying hens in many countries.

Mechanism of action of permethrin

Synthetic pyrethroids, including permethrin, have a similar mode of action as organochlorines. They act on the membrane of nerve cells blocking the closure of the ion gates of the sodium channel during re-polarization. This strongly disrupts the transmission of nervous impulses. At low concentrations insects suffer from hyperactivity. At high concentrations they are paralyzed and die.

Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.