A semisynthetic macrolide antibiotic of the avermectin family of compounds, effective in the treatment of filariasis and many other parasites. The drug destroys Onchocerca microfilaria and Filaria bancrofti. Derived from the soil bacterium, Streptomyces avermitilis. Approved by the FDA for the treatment of scabies by topical administration. Widely used in veterinary medicine in a number of species for control of ectoparasites and endoparasites. Unusual sensitivity (increased toxicity, and sometimes death) in collie-type breeds is well documented.