of the cyclopropane ring in addition to that of the double bond. This led to the initial commercialisation of cyhalothrin, under the trade name Grenade, but the resulting material was still a mixture of four isomers owing to the racemic nature of the Z-cis acid and because the alpha-cyano group was a 1:1 mixture of possible R and S configurations. The process work made available a relatively large supply of the Z-cis acid and hence allowed two further commercially important steps to be taken. The first was to make the development and sales of tefluthrin feasible and the second was to spur research directed at making compositions of cyhalothrin with fewer isomers in the sales product. After further research and field tests, ICI chose to focus on λ-cyhalothrin, the mixture containing the single most active isomer together with its mirror image. This so-called "enantiomer pair", ICI code number PP321, could be used after a process for its economic production and purification was developed using crystallisation with recycling of the unwanted enantiomer pair. The new product was first launched in nine countries in 1985 using the trademark Karate. At that time, γ-cyhalothrin, ICI code number PP345, was not a feasible alternative product owing to the difficulty of manufacturing that isomer alone, especially if this involved recycling the "wrong" isomer of the Z-cis acid. In 2000, the agrochemical business of ICI merged with that of Novartis to form Syngenta, which still manufactures and supplies λ-cyhalothrin. The patents covering the parent compound expired in most major markets in 2003. FMC has entered the market as a supplier of γ-cyhalothrin for use as a broad-spectrum insecticide under the brand name Scion. Mechanism of action Pyrethroids, including cyhalothrin, disrupt the functioning of the nervous system in an organism. They are fast-acting axonic excitotoxins, the toxic effects of which are mediated by preventing the closure of the voltage-gated sodium channels in axonal membranes. The sodium channel is a membrane protein with a hydrophilic interior. This interior is shaped precisely to allow sodium ions to pass through the membrane, enter the axon, and propagate an action potential. The binding of the insecticide to the protein keeps the channels in their open state, so the nerves cannot repolarize, thereby paralyzing the organism. One consequence of the mode of action is that cyhalothrin has useful knockdown properties. That is, affected larvae rapidly cease feeding and may fall off the