Fenbendazole (often abbreviated FBZ) is used in both large and small animals. In dogs, it is useful against roundworms, hookworms, and the more difficult to treat whipworms. It is effective against the Taenia species of tapeworm but not against the common tapeworm, Dipylidium caninum. It is also effective against Giardia (an intestinal protozoan that causes diarrhea) as well as several species of lungworm and even some flukes.