Eprinomectin B1a is a semi-synthetic analogue of avermectin B1a prepared by oxidation of the 4''-hydroxy moiety and reductive amination followed by acetylation. Eprinomectin B1a is the major component (>90%) of the commercial product for endo- and exo-parasite control, eprinomectin. The avermectins and milbemycins are also potent insecticides and acaricides.