Cyphenothrin is one of the type II pyrethroid insecticide, in combination with fipronil it used to provide dogs with protection to common topical parasites in dogs. Cyphenothrin primarily affects sodium channels in excitable membranes causing a prolongation of the sodium current during excitation. The prolonged sodium current results in the development of a depolarizing after potential following the action and is responsible for the induction of repetitive activity, which is the most characteristic effect of pyrethroid poisoning in the nervous system. At low concentrations, insects and other arthropods suffer from hyperactivity. At high concentrations, they are paralyzed and die.

Cyphenothrin, (+)-trans- (d,d,trans-cyphenothrin) is the type II pyrethroid insecticide, acting by contact poisoning Cyphenothrin, (+)-trans- is used in public health against flies, mosquitoes, cockroaches, etc. Cyphenothrin is the ISO common name for a racemic mixture of 4 pairs of diastereoisomers, designated as (±)-α-cyano-3- phenoxybenzyl (±)-cis-trans- chrysanthemate. The name Cyphenothrin, (+)-trans- refers to an enantio-enriched mixture, comprised mainly of the single stereoisomer (S)-α-cyano-3- phenoxybenzyl (1R, 3R)-2,2-dimethyl-3-(2-methylprop-1-enyl) cyclopropanecarboxylate, with only small proportions of the other stereoisomers, as defined by the WHO specification. Cyphenothrin, (+)-trans- is almost insoluble in water but highly soluble in organic solvents, such as hexane, ethanol, acetone, toluene etc. Cyphenothrin, (+)-trans- stable under normal storage conditions but is readily hydrolyzed in water at higher pH and is sensitive to light. Cyphenothrin, (+)-trans- has a low potential for bioaccumulation due to hydrolysis, photolysis and metabolism in water, soil and in biota. The data for toxicology of Cyphenothrin, (+)-trans- partly rely on studies conducted with cyphenothrin. Cyphenothrin, (+)-trans- generally shows low mammalian toxicity and is not a sensitizer in the Buehler and is not irritating to the rabbit eye and skin. There was no evidence of carcinogenicity in the rat or mouse. There was no evidence of mutagenic responses in bacterial, micronucleus or sister chromatid exchange tests. In a 2-generation reproduction study in the rat, no reproductive effects were observed at any dose level. There was no evidence of teratogenicity or developmental effects in rats or rabbits, although there was a decrease in maternal weight gain and a consequential decrease in rat offspring viability at the high dose tested. Cyphenothrin, (+)-trans- is very toxic to Daphnia magna and fish but it has a low toxicity to bobwhite quails. On the basis of the one-year dog study, a NOEL of 16.8 to 19.6 mg/kg bw/d is established by the Swiss Office of Public Health. The Cyphenothrin, (+)-trans- TC was classified as moderately toxic (Class 3) in Switzerland and, although it has not been classified by the International Programme on Chemical Safety (IPCS), this organization has classified the closely related cyphenothrin (1R-isomers) as Class II, moderately hazardous.