An injectable macrocylic lactone antiparasitic used for control of Dirofilaria immitis heartworm and Ancylostoma caninum hookworms in heartworm-negative dogs; effect lasts 6 months; a semisynthetic avermectin class derivative of nemadectin isolated from Streptomyces cyaneogriseus subsp. noncyanogenus; less toxic in Collies then ivermectin; also used in horses as an oral gel and in cattle as topical solution; good especially for encysted small strongyles in horses. Mechanism of action is to enhance glutamate gate chloride channel permeabilty of membranes and increase gamma amino butyric acid at presynaptic membranes in nematode and arthropod nerve cells; leads to parasite paralysis and death. Not effective against flukes or tapeworms.