Fipronil
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Fipronil, or Termidor, is a broadspectrum insecticide that disrupts the insect's central nervous system by blocking the passage of chloride ions through the GABA receptor and glutamate receptor (GluCl), inhibitors 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 mammalians (Raymond-Delpech et coll., 2005). Termidor is a BASF brand name for Fipronil.
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 through out the colony. With the cascading effect, the projected kill rate is about 95% in 3 days for ants and cockroaches.
Fipronil is used as the active ingredient in Frontline, a topical flea control commonly used on dogs and cats. It kills adult fleas before they lay eggs and claims to kill ticks at the larval, nymphal, and adult stages. Sebaceous glands in the skin serve as the reservoir and therefore does not become systemic.
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. In the US, commercial strength ant Fipronil based gels are sold under the MaxForce brand, and the consumer strength is sold under the Combat brand.
It acts by binding to an allosteric site of GABA a 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 humans, fipronil poisoning is characterized by vomiting, agitation, and seizures, and can usually be managed through supportive care and early treatment of seizures (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). This risk may be associated with the withdrawal of the MaxForce tick management product.
The IUPAC chemical name for Fipronil is 5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-(trifluoromethylsulfinyl)-1H-pyrazole-3-carbonitrile, and its empirical formula is C12H4Cl2F6N4OS.
Raymond-Delpech V, Matsuda K, Sattelle BM, Rauh JJ, Sattelle DB (2005) Ion channels: molecular targets of neuroactive insecticides. Invert Neurosci:1-15.
