Eprinomectin B1b is a semi-synthetic analogue of avermectin B1b prepared by oxidation of the 4”-hydroxy moiety and reductive amination followed by acetylation. Eprinomectin B1b is the minor component (<10%) of the commercial product for endo- and exo-parasite control, eprinomectin. Members of the avermectin/milbemycin class exert their anthelmintic effects by binding to glutamate-gated chloride channels expressed on nematode neurones and pharyngeal muscle cells. The avermectins and milbemycins are also potent insecticides and acaricides.