Ectoparasitic preparation

The first commercially available HCH insecticide sometimes misleadingly called benzene hexachloride (BHC) was a mixture of isomers, principally alpha HCH (65-70%), beta HCH (7-10%), and gamma HCH (14-15%). Most of the insecticidal activity was due to the gamma isomer (Figure 5.1), a purified preparation of which (>99% pure) was marketed as lindane. In Western countries, technical HCH was quickly replaced by lindane, but in some other countries (e.g., China) the technical product, which is cheaper and easier to produce, has continued to be used. HCH has been used as a seed dressing, a crop spray, and a dip to control ectoparasites of farm animals. It has also been used to treat timber against wood-boring insects. 

Ivermectin is exceptionally effective in very low dosages against nematodes and arthropod parasites in cattle and has been widely used for treatment of endo-and ectoparasites in cattle, sheep, goats, and swine (49). It is administered orally, parenterally, or as a pour-on preparation at dosages ranging from 0.2 to 0.6 mg/ kg bw. Ivermectin exhibits teratogenic effects in rat, rabbit, and mouse. 

Mevinphos (96, Phosdrin ) is prepared from methyl 3-chloroacetoacetate in reaction with trimethyl phosphite. Mevinphos (Phosdrin ) is a mixture of Z and E stereoisomers in which the Z isomer was found to be 100 times more active.54 In contrast to mevinphos, E and Z isomers of bromfenvinphos (92) and chlorfenvinphos (94) show no significant difference for a number of biological properties for insecticides.55 The less toxic Clodrin (98) is synthesized from the 1-phenylethoxy ester of 3-chloracetoacetate 97 which is used for control of ectoparasites in horses, cattle, sheep, and swine.54... 

---