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

Common name: FENVALERATE

Type: pesticide
Chemical class: synthetic pyrethroid


Molecular structure of FENVALERATE





Type of action: Broad spectrum contact, non systemic ectoparasiticide: insecticide, louisicide, acaricide, tickicide
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. National regulatory authorities determine whether a product is approved for a given indication, i.e. use on a particular host at a specific dose and against a specific parasite. Check the labels of the products available in your country.

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


Oral LD50, rat, acute*:  451 mg/kg
Dermal LD50, rat, acute*: >5000 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.

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

WARNING: Most synthetic pyrethroids can be toxic for cats.

MRL (maximum residue limit) established 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 established also for agricultural pesticides that are not approved for use on animals but are used on commodities fed to animals. It may be also established 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.

General safety information for 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: SUMITOMO, SHELL
Some original brands: TIRADE, SUMIFLY
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, very scarce
Use in HORSES: Yes, very scarce
Use in

Main delivery forms: 

Use in human medicine: No
Use in
public/domestic hygiene: Yes
Use in
agriculture: Yes
Generics available: 
Yes, very few for veterinary use


On livestock & horses: Yes, as for all synthetic pyrethroids: very frequent worldwide in such species as cattle ticks (Boophilus spp), horn flies (Haematobia irritans), sheep lice (Damalinia ovis), houseflies (Musca domestica), mosquitoes.

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


Fenvalerate is a synthetic pyrethroid particularly effective against insects (flies, lice, mosquitoes, etc.) but only mediocre against ticks and mites. As most synthetic pyrethroids, fenvalerate is a mediocre larvicide, i.e. it is not indicated for the large-scale prevention of cutaneous myiases ((e.g. screwworms, blowfly strike, etc.) with sprays, pour-ons, etc.

Fenvalerate is a mixture of various optic isomers with different insecticidal efficacy. Commercial products may contain different isomer mixtures. 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.

Although patent has expired long ago, there are only a few generic veterinary products available.

However, resistance to fenvalerate is widespread and can be very high in 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 fenvalerate are already totally useless against such parasites in many places. The same applies to all other synthetic pyrethroids (e.g. cypermethrin, deltamethrin, flumethrin, permethrin, etc.). And this is true for whatever delivery form: dipping, spraying, pour-ons, etc.

Pharmacokinetics of fenvalerate

Topically administered fenvalerate 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 fenvalerate 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 fenvalerate through licking or grooming. A large amount of it is excreted unchanged through the feces. The absorbed fenvalerate is quickly metabolized in the liver to inactive metabolites that are excreted through urine. This is done by a specific enzyme called glucuronidase. However, cats lack this enzyme and cannot properly metabolize most synthetic pyrethroids. This is why most synthetic pyrethroids are toxic to cats.

Mechanism of action of fenvalerate

Synthetic pyrethroids, including fenvalerate, 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.