Milbemycin A4 oxime is a semi-synthetic macrocyclic lactone prepared by the oxidation and oximation of milbemycin A4. Milbemycin A4 oxime is the major component (~70%) in the commercial product, milbemycin oxime, marketed for endo- and exo-parasite infections. Like the other milbemycin/avermectins, milbemycin A4 oxime acts by opening glutamate sensitive chloride channels in neurons of invertebrates, leading to paralysis by hyperpolarisation of these cells and signal transfer blocking.