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IUPAC name
Other names Fipronil
CAS number 120068-37-3 Yes check.svgY
PubChem 3352
ATCvet code QP53AX15
Molecular formula C12H4Cl2F6N4OS
Molar mass 437.15 g/mol
Density 1.477-1.626 g/cm³
Melting point

200.5 °C

 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Fipronil is a broad spectrum insecticide that disrupts the insect central nervous system by blocking the passage of chloride ions through the GABA receptor and glutamate-gated chloride channels (GluCl), components of the central nervous system. This causes hyperexcitation of contaminated insects' nerves and muscles. Insect specificity of fipronil may come from a better efficacy on GABA receptor but also on the fact that GluCl does not exist in mammals.[1]

Fipronil is a slow acting poison. When mixed with a bait it allows the poisoned insect time to return to the colony or haborage. In cockroaches the feces and carcass can contain sufficient residual pesticide to kill others in the same nesting site. In ants, the sharing of the bait among colony members assists in the spreading of the poison throughout the colony. With the cascading effect, the projected kill rate is about 95% in 3 days for ants and cockroaches.

Toxic baiting with Fipronil has also been shown to be extremely effective in locally eliminating German wasps (Yellow jacket). All colonies within foraging range are completely eliminated within one week.[2] Unlike broadcast applications, this application does not expose beneficial insects such as honeybees to the pesticide.

Wildlife impacts include the following:

  • Fipronil is highly toxic to fish and aquatic invertebrates. Its tendency to bind to sediments and its low water solubility may reduce the potential hazard to aquatic wildlife (2,4).
  • Fipronil is toxic to bees and should not be applied to vegetation when bees are foraging (2).
  • Fipronil has been found to be highly toxic to upland game birds, but is practically non-toxic to waterfowl and other bird species (2,4). One of the metabolites of fipronil has a higher toxicity to birds than the parent compound itself (4).

Fipronil is used as the active ingredient in Effipro (Virbac), Frontline Top Spot (Merial) at about 9.8% concentration. Fipronil is also used together with (S)-methoprene (8.8%) in Frontline Plus (Merial), a topical flea and tick control commonly used on dogs and cats. It kills adult fleas before they lay eggs (within 24 hours). It is also the active ingredient in GardenTech's Over N Out season long fire ant control product.

After a local application of Effipro/Frontline, fipronil is slightly absorbed (approx. 15%) through the skin. Low levels of fipronil may be detected in the plasma, with a very high variability between dogs.[3]

It is also the active ingredient of Regent, now marketed by BASF, which also sells Fipronil under the brand name Termidor for use as a conventional barrier treatment for termites and also as a dust to be blown into termite tunnels. In the US, ant Fipronil based gels are sold under the MaxForce brand (mfg. Bayer), and under the Combat brand (mfg. Dial Corp). Both brands carry .01% Fipronil by weight as the active ingredient. Agricultural products include Chipco Choice for use against pests of field corn, golf courses and commercial turf.

It acts by binding to an allosteric site of GABAA receptors and GluCl receptor (of the insect), a form of non-competitive inhibition.

Acute oral LD50 (rat) 97 mg/kg
Acute dermal LD50 (rat) >2000 mg/kg

In animals and humans, fipronil poisoning is characterized by vomiting, agitation, and seizures, and can usually be managed through supportive care and early treatment of seizures.[4] [5] This risk may be associated with the withdrawal of the MaxForce tick management product.[6]

Fipronil is a possible carcinogen and a potential ground water contaminate. It is a suspected endocrine disruptor. In animals and humans, fipronil poisoning is "moderate" in terms of acute (immediate) toxicity. Source: In May 2003, the DGAL (Direction Générale de l'Alimentation du ministère de l'Agriculture ) indicated a case of bee mortality observed in Southern France related to Fipronil acute toxicity. Intoxication was linked to defective seed treatment, which generated dust. The seed treatment involved has since been forbidden. Fipronil was used in a broad spraying to control locusts in Madagascar in a program that began in 1997 [7].

Fipronil was first developed by Rhone-Poulenc and patented under the US Patent No. US 5,232,940 B2. Since 2003, BASF holds the patent rights for producing and selling Fipronil based products in many countries.

Cancer classification: The U.S. EPA classified fipronil as a Group C - Possible Human Carcinogen, based on “increases in thyroid follicular cell tumors in both sexes of the rat.”

No human data were found on the teratogenic or reproductive effects of fipronil.

The chronic reference dose (RfD) for fipronil is 0.0002 mg/kg/day based on the NOAEL for chronic toxicity (0.5 ppm or 0.019 mg/kg/day) and an uncertainty factor of 100

Reference Dose (RfD): The RfD is an estimate of the quantity of chemical that a person could be exposed to every day for the rest of their life with no appreciable risk of adverse health effects. The reference dose is typically measured in milligrams (mg) of chemical per kilogram (kg) of body weight per day. Exposure: Effects of fipronil on human health and the environment depend on how much fipronil is present and the length and frequency of exposure. Effects also depend on the health of a person and/or certain environmental aspects.

A spot-on treatment study in dogs and cats detected 14C-fipronil concentrated in the sebaceous glands, epithelial layers surrounding the hairs, and exposed part of the hair shaft 2 months after treatment, suggesting the passive diffusion of fipronil in the sebum covering hair and skin.

Fipronil applied to foliage partially photodegrades to form fipronil-desulfinyl

Fipronil and fipronil-desulfinyl are less volatile than water and can concentrate under field conditions.

Fipronil-sulfone, the primary biological metabolite of fipronil, is reported to be twenty times more active at mammalian chloride channels than at insect chloride channels. Fipronil-sulfone is reportedly six times more potent in blocking vertebrate GABA-gated chloride channels than fipronil, but demonstrates similar toxicity to the parent compound in mammals.

Fipronil-desulfinyl, the primary environmental metabolite (photoproduct) of fipronil, is 9-10 times more active at the mammalian chloride channel than the parent compound, reducing the selectivity between insects and humans when exposed to this metabolite.

The primary metabolite of fipronil in armyworms, mice, and presumably other insects and vertebrates is the fipronil sulfone derivative. Researchers injected mice with fipronil and detected the sulfone derivative in the brain, liver, kidney, fat, and feces.

Fipronil-desulfinyl, the primary photodegradate of fipronil, has been measured in the fat, brain, liver, kidney, skin, and feces of mice, rats and lactating goats after oral exposure or injection.

Fipronil was not among the pesticides included for biomonitoring assessment in the third National Health and Nutrition Examination Survey (NHANES)

Fipronil was measured in surface water at concentrations of 0.829 to 5.290 µg/L in southwestern Louisiana during March through April, which corresponds to the timing of releases of ricefield tailwater. Results indicate that fipronil degradation products accumulate in riverbed sediment while the parent compound does not.

Fipronil-sulfone is 6.3 and 3.3 times more toxic to rainbow trout and bluegill sunfish, respectively, than the parent compound.

Fipronil accumulates in fish with a bioconcentration factor of 321 for whole fish, 164 for edible tissue, and 575 for non edible tissue.

Fipronil is highly toxic to freshwater invertebrates. In daphnids, the NOEL for fipronil was measured at 9.8 µg/L, and the LOEL was 20.0 µg/L. The fipronil-sulfone and fipronil-desulfinyl metabolites are 6.6 and 1.9 times more toxic to freshwater invertebrates, respectively, than the parent compound.

Fipronil is highly toxic to oysters with an EC 50 of 0.77 mg/L and very highly toxic to mysid shrimp with a 96-hour LC 50 of 140 ng/L. Exposure to less than 5.0 ng/L fipronil affected mysid growth, reproduction, and survival.

The fipronil-sulfone metabolite is highly toxic to upland game birds and moderately toxic to waterfowl by ingestion.

Fipronil is highly toxic to honeybees by contact and ingestion when applied to plant foliage.

Researchers found that fipronil killed 38.8-94.5% of beneficial predators such as Orius spp. (flower bug) and Geocoris spp. (big-eyed bug) and significantly reduced reproductive success and prey consumption when applied at labeled rates.

When applied to fields for locust control, fipronil killed >90% of the resident nontarget insects Carabidae, Tenebrionidae, Scelionidae, and Sphecidae populations in 2 days. Recolonization was very poor for 2–4 weeks, depending on the applica- tion rate.


  1. ^ Raymond-Delpech V, Matsuda K, Sattelle BM, Rauh JJ, Sattelle DB (2005) Ion channels: molecular targets of neuroactive insecticides. Invert Neurosci: 1-15.
  2. ^ Paula Sackmann, Mauricio Rabinovich and Juan Carlos Corley J. Econ. Entomol. (2001). "Successful Removal of German Yellowjackets (Hymenoptera: Vespidae) by Toxic Baiting." (PDF). pp. 94(4):811-816.  
  3. ^ Veterinary Medicines Directorate (2004). "Summary of Product Characteristics for Frontline Spot On Dog".  
  4. ^ Ramesh C. Gupta (2007). "Veterinary Toxicology". pp. 502–503.,M1.  
  5. ^ Mohamed F, Senarathna L, Percy A, Abeyewardene M, Eaglesham G, Cheng R, Azher S, Hittarage A, Dissanayake W, Sheriff MH, Davies W, Buckley NA, Eddleston M., Acute human self-poisoning with the N-phenylpyrazole insecticide fipronil--a GABAA-gated chloride channel blocker, J Toxicol Clin Toxicol. 2004;42(7):955-63)
  6. ^ Natural Resource Consultants, Inc. (March 2007). "Deer Management Plan for the Crum Woods of Swarthmore College" (PDF). pp. 40.  
  7. ^ June 2000 BBC News story "Anti-locust drive 'created havoc'"

<Hainzl, D.; Cole, L. M.; Casida, J. E. Mechanisms for Selective Toxicity of Fipronil Insecticide and Its Sulfone Metabolite and Desulfinyl Photoproduct. Chem. Res. Toxicol. 1998, 11, 1529-1535.> <Zhao, X.; Yeh, J. Z.; Salgado, V. L.; Narahashi, T. Sulfone metabolite of fipronil blocks gamma-aminobutyric acid- and glutamate-activated chloride channels in mammalian and insect neurons. J. Pharmacol. Exp. Ther. 2005, 314 (1), 363-73.> <Hainzl, D.; Casida, J. E. Fipronil insecticide: Novel photochemical desulfinylation with retention of neurotoxicity. Proc. Natl. Acad. Sci. 1996, 93, 12764-12767.> <Tomlin, C. D. S., The Pesticide Manual, A World Compendium, 14th ed.; British Crop Protection Council: Hampshire, England, 2006; pp 462–464> <New Pesticide Fact Sheet - Fipronil; EPA 737-F-96-005; U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, U.S. Government Printing Office Washington, DC, 1996; pp 1–10. > </CDC. Third National Report on Human Exposure to Environmental Chemicals; U.S. Department of Health and Human Services, Centers for Disease Control and Prevention: Atlanta, 2005.> <Fipronil and Degradation Products in the Rice-Producing Areas of the Mermentau River Basin, Louisiana, February-September 2000; USGS Fact Sheet FS-010-0; U.S. Department of the Interior, U.S Geological Survey. http://la.water.usgs. gov/pdfs/NAWQA-fipronil.pdf (accessed Oct 2007) updated March 2003.> <Elzen, G. W. Lethal and Sublethal Effects of Insecticide Residues on Orius insidiosus (Hemiptera: Anthocoridae) and Geocoris punctipes (Hemiptera: Lygaeidae). J. Econ. Entomol. 2001, 94, 55-59.> <Balanca, G.; de Visscher, M.-N. Impacts on Nontarget Insects of a New Insecticide Compound used Against the Desert Locust (Schistocerca gregaria (Forskal 1775)). Arch. Environ. Contam. Toxicol. 1997, 32, 58-62> <Fipronil  : Third Reevaluation - Report of the Hazard Identification Assessment Review Committee; HED Doc. No. 014400; U.S. Environmental Protection Agency, Health Effects Division, U.S. Government Printing Office: Washington, DC, 2000; pp 1–24. > <Birckel, P.; Cochet, P.; Benard, P.; Weil, A. Cutaneous Distribution of 14C-Fipronil in the Dog and in the Cat Following a Spot-On Administration; Third World Congress of Veterinary Dermatology: Edinburgh, Scotland, 1996.>

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