Fenbendazole Ivermectin bolus is a combination veterinary medication used to treat parasitic infestations in animals. This bolus formulation combines two active ingredients: fenbendazole and ivermectin.Fenbendazole is an anthelmintic drug that works by disrupting the metabolism of parasites, ultimately leading to their elimination. It is effective against a wide range of internal parasites, including roundworms, hookworms, whipworms, and certain types of tapeworms.