Fipronil- A Phenylpyrazole Pesticides


Fipronil is in the phenylpyrazole class of pesticides. It was recently developed in response to the increase resistance of insects to pesticides. Fipronil is a broad-spectrum insecticide that belongs to the family of phenylpyrazole chemicals. Fipronil is the name for the chemical [5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-fluoromethylsulfinyl pyrazole].

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Fipronil is found in many pesticide products including:

  • gel baits
  • granular products for grass
  • products for liquid termite control
  • spot-on pet care products and insecticide products for agriculture

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Fipronil is known to be more effective against certain species of insects that are resistant to most insecticides. It is more effective than other insecticides such as organophosphate, carbamate and pyrethroids against species of coleopteran, orthoptera and lepidoptera.

Fipronil is used in the control of insects and worms including:

  • Cockroaches
  • beetles, ants
  • fleas, termites
  • ticks, weevils
  • mole crickets
  • rootworms

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Mechanism of action involve a noncompetitive binding to glutamate-activated chloride (GABAA gated chloride) channels. It blocks the inhibitory action of GABAA in the central nervous system resulting in hyperexcitation at low doses. Paralysis and death of insects occur at higher doses. Fipronil shows a more than 500-fold selective toxicity action in insects when compared to mammals because of the differences in affinity of receptor binding between receptors in insect and receptors in mammals.



Once in the body, fipronil is found mainly in the fatty tissue, and breaks down into smaller chemicals called metabolites. Pharmacokinetic studies carried out in rats showed that fipronil metabolites (sulfone and desulfinyl) is excretes mainly in the feces (45–75%) and little in the urine (5–25%).



People can be exposed to the fipronil chemical through:

  • Direct skin contact: Skin contact may occur in humans while applying the fipronil products.
  • Inhalation: Breathing chemical into the body
  • Oral ingestion: People may inadvertently swallow fipronil with food if they do not wash their hands after skin exposure occurred. Cases of fipronil self-poisoning have also been reported



The effect of exposure to fipronil in humans varies depending on the mode of exposure:

Skin: contact can result in skin irritation and atopic dermatitis.

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Atopic dermatitis caused by Fipronil


Oral ingestion: When ingested reported health effects included:

  • nausea
  • vomiting
  • stomach ache
  • sweating, headache
  • dizziness
  • generalized body weakness



  • Atopic dermatitis caused by Fipronil will resolve with time
  • The symptoms and signs from inadvertent oral ingestion of fipronil with food will resolve and people get improvement in health with minimal treatment
  • In fipronil self-poisoning minimal resuscitation and supportive care is required for a favorable outcome.
  • Fipronil has a low toxicity level. Gastric emptying procedures are not of value following fipronil self-poisoning
  • The use of ipecac to manage fipronil self-poisoning is contraindicated because of the risk of seizures



The residue of fipronil or its metabolites can be detected in the body tissue, urine and feces. This can be used as biomarker of fipronil exposure.



Research done on rats fed with fipronil for two years showed that it caused thyroid tumors in rats fed high dose of fipronil. Fipronil is classified as a possible human carcinogen. Long term exposure of rats to fipronil was found to affect fertility. Long-term studies carried out in humans have not shown any effect of fipronil on fertility.



National Pesticide Information Center (NPIC). Fipronil general fact sheet. Accessed from:

Vidau, C., Brunet, J.L., Badiou, A., & Belzunces, L. P. Phenylpyrazole insecticides induce cytotoxicity by altering mechanisms involved in cellular energy supply in the human epithelial cell model Caco-2. Toxicology in Vitro, 23(4), 589–597.

Mossa, A.T. H., Swelam, E. S., & Mohafrash, S. M. M. (2015). Sub-chronic exposure to fipronil induced oxidative stress, biochemical and histopathological changes in the liver and kidney of male albino rats. Toxicology Reports, 2, 775–784.

Gupta, R. C. & Milatovic D. (2014). Biomarkers in Toxicology: Fipronil- an overview. ScienceDirect Topics. Retrieved from:

Mohamed, F., Senarathna, L., Percy, A., Abeyewardene, M., Eaglesham, G., Cheng, R., … Eddleston, M. (2004). Acute human self-poisoning with the N-phenylpyrazole insecticide fipronil–a GABAA-gated chloride channel blocker. Journal of toxicology. Clinical toxicology, 42(7), 955–963.



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