Flumethrin is a type II synthetic pyrethroid insecticide used externally in veterinary medicine against parasitic insects and ticks on cattle, sheep, goats, horses, and dogs, and the treatment of parasitic mites in honeybee colonies. In veterinary medicine, it is applied topically to sheep, cattle, and goats, as a 1% w/v pour-on or as a plunge dip for the control of ticks, lice, and mites. The pour-on is applied at a rate of 2 mg/kg BW. The plunge dip is diluted at a rate of 1-litre product in 900 liters water. For control of scab, the sheep must be dipped for one minute. Plastic strips impregnated with 3.6 mg Flumethrin are hung in beehives for the diagnosis and treatment of varroatosis in honeybees. Four strips per hive are used for mature colonies and 2 per hive for immature colonies. Flumethrin causes a long-lasting prolongation of the normally transient increase in sodium permeability of the nerve membrane during excitation, resulting in long-lasting trains of repetitive firing. The cyano group on the phenoxy-fluorobenzyl alcohol moiety is considered to be responsible for the long-lasting prolongation of sodium permeability. The type II pyrethroids produce a distinct poisoning syndrome which is characterized by choreoathetosis (sinuous writhing of the whole body) and salvation. Flumethrin on the membrane of nerve cells blocking the closure of the ion gates of the sodium channel during re-polarization. This strongly disrupts the transmission of nervous impulses, causing spontaneous depolarization of the membranes or repetitive discharges. At low concentrations insects and other arthropods suffer from hyperactivity. At high concentrations, they are paralyzed and die. Sensory and nervous cells are particularly sensitive. Flumethrin is a complex mixture of stereoisomers. The molecule contains three asymmetric carbon atoms, there is cis-trans isomerism at the cyclopropane ring and cis-trans isomerism at the carbon-carbon double bond of the alkene. So there are 16 different isomers. Commercial Flumethrin typically contains 92% of the trans isomers on the cyclopropane ring and the cis-configuration at the olefinic carbon-carbon double bond and 8% of the isomer with cis geometry on the cyclopropane ring and the cis-configuration at the olefinic carbon-carbon double bond.