Fipronil is an antiparasitic active ingredient used in veterinary medicine in dogs, cats and livestock against external parasites (fleas, fliesticks, lice, mites, etc.). It is also used against agricultural and household pests. It belongs to the chemical class of the phenylpyrazoles.

Common name: FIPRONIL

Type: pesticide
Chemical class: phenylpyrazole


Molecular structure of FIPRONIL






Type of action: Broad-spectrum, contact, non-systemic ectoparasiticide: insecticide, tickicide, louisicide
Main veterinary parasites controlled: fleas, ticks, liceflies, 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 fipronil used in domestic animals.


Oral LD50, rat, acute*:  97 mg/kg
Dermal LD50, rat, acute*: >200 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.

MRL (maximum residue limit) set for animal tissues (e.g. 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. An MRL for meat 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.

Learn more about fipronil safety.

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: 1990
Introduced by: RHÔNE-MÉRIEUX (→ MERIAL)
Some original brands: FRONTLINE
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, scarce, but increasing in Latin America
Use in
DOGS and CATS: Yes, massive: Fipronil is today's most used active ingredient against fleas on pets worldwide.

Main delivery forms: 

Use in human medicine: No
Use in public/domestic hygiene: Yes
Use in
agriculture: Yes
Generics available: 
Yes, a lot


With fipronil alone

With fipronil + other active ingredients


In livestock: Yes, on cattle ticks (Boophilus microplus), probably with cross-resistance to organochlorines and permethrin.
In pets: Not really, yet

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


Fipronil is a rather modern "classic" synthetic insecticide introduced in the early 1990's. Fipronil is massively used in dogs and cats for flea and tick control, especially after patent expiry in the 2000', when dozens of generics flooded the market in many countries. Interestingly, even large multinationals that have their "own" flea or tick control products have introduced brands with generic fipronil in many countries. It is often used in mixtures with insect development inhibitors.

There are also livestock pour-ons with fipronil in many Latin American countries, mainly for cattle against horn flies and cattle ticks (Boophilus microplus), but not in the US, the EU or Australia. Interestingly, MERIAL introduced such a product in Brazil in the late 1990's, and later on in other Latin American countries. Such fipronil pour-ons have withholding periods of 100 and more days!

Efficacy of fipronil

In dogs and cats, fipronil applied as a spot-on is highly effective against fleas and several tick and lice species. But not against all ticks and lice species that can infest dogs and cats. Efficacy against fleas is comparable to that of other modern insecticidal active ingredients such as imidacloprid, pyriprolespinetoram or spinosad. The insect development inhibitors (e.g. methoprene, pyriproxyfen) often added to the formulation target the immature stages of the fleas that develop off the animals in the domestic environment of the pets.

In livestock fipronil is so far exclusively used against cattle ticks (Boophilus microplus) and horn flies (Haematobia irritans). It is a quite popular alternative in regions where these two important parasites have developed high resistance to synthetic pyrethroids and organophosphates.

Pharmacokinetics of fipronil

Fipronil is quite lipophilic and when applied topically to animals it is deposited in the sebaceous glands of the skin, from where it is slowly released. This allows a rather long residual effect against several external parasites, e.g. fleas and ticks.

Absorption of topically administered fipronil is rather low in dogs and cats, usually not more than 5% of the administered dose. The absorbed fipronil is found predominantly in fatty tissues. The primary metabolite is the sulfone derivative, which is substantially more toxic, both for parasites and for mammals.

Excretion of absorbed fipronil occurs mainly through the feces. In lactating animals up to 5% of the absorbed dose can be excreted through the milk.

Mechanism of action of fipronil

Phenylpyrazoles are inhibitors of GABA (gamma-aminobutyric acid), a key neurotransmittor in the central nervous system. This mechanism exists not only in insects but also in mammals and other vertebrates. However phenylpyrazoles seem to be much less effective on GABA receptors in vertebrates than in invertebrates.

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