Pyrethroid
Definition
Synthetic analogues of natural pyrethrins (deltamethrin, cypermethrin, permethrin, fenvalerate). Act on voltage-gated sodium channels like OC but break down quickly in mammals, giving them a wide safety margin.
- Origin
- Synthetic analogues of natural pyrethrins
- Examples
- Deltamethrin, cypermethrin, permethrin, fenvalerate
- Mechanism
- Voltage-gated sodium channel disruption
- Mammalian safety margin
- Wide, due to rapid metabolic breakdown
- Shares mechanism with
- Organochlorine insecticides
Common questions
Why do pyrethroids pose lower risk in human poisoning cases compared to organochlorines?+
Mammals metabolise pyrethroids quickly through ester hydrolysis and oxidation, clearing them from the body well before they accumulate to toxic levels, whereas organochlorines resist breakdown and persist in fatty tissue for extended periods.
How does a toxicologist distinguish pyrethroid exposure from organophosphate exposure in a case?+
Pyrethroids do not inhibit acetylcholinesterase, so a case with normal cholinesterase activity but symptoms of sodium-channel disruption such as tremor or paraesthesia points toward pyrethroid rather than organophosphate involvement.
Are pyrethroids toxic to non-mammalian species at the doses used against insects?+
Yes. Fish and many aquatic invertebrates lack the rapid metabolic clearance mammals have, so pyrethroids remain highly toxic to aquatic life even at concentrations considered safe for humans and other mammals.
Related terms
- AChE / BChE
- Acetylcholinesterase (RBC membrane bound, true cholinesterase) and butyrylcholinesterase (plasma, pseudo-cholinesterase). Both depressed in OP and carbamate exposure; plasma BChE falls first and...
- Aluminium Phosphide (AlP)
- Solid grain-fumigant rodenticide sold as Celphos, Quickphos, Sulfas tablets. On contact with moisture or stomach acid, releases phosphine (PH3) gas, which blocks...
- Carbamate
- Carbamic-acid ester insecticides (carbaryl, carbofuran, propoxur, aldicarb). Reversibly inhibit acetylcholinesterase by carbamylating the active-site serine; spontaneous decarbamylation makes oximes unnecessary and sometimes...
- Ellman Method
- Standard spectrophotometric cholinesterase assay. Acetylthiocholine substrate plus 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) yields a yellow 5-thio-2-nitrobenzoate anion read at 412 nm. The rate of...
- Organochlorine (OC)
- Chlorinated hydrocarbon insecticides (DDT, BHC/lindane, endosulfan, dicofol, aldrin, dieldrin). Highly lipophilic, neurotoxic via voltage-gated sodium channel disruption, and persistent in fat and...
- Organophosphate (OP)
- A class of insecticides (monocrotophos, chlorpyrifos, methyl parathion, dichlorvos, phorate) that inhibit acetylcholinesterase, producing the cholinergic toxidrome. The dominant suicidal poison in...
- QuEChERS
- Quick, Easy, Cheap, Effective, Rugged and Safe sample-prep protocol for pesticide residues. Acetonitrile extraction, MgSO4 + NaCl partition, dispersive SPE clean-up with...