Closantel is a synthetic anti parasitic agent which is highly effective against adults and larvae (6 to weeks old) of liver flukes (Fasciola hepatica), and against several important gastrointestinal roundworms (e.g. Bunostomum, Haemonchus, Oesophagostomum, Ostertagia - Teladorsagia, Strongyloides, Trichostrongylus), as well as against screwworms (maggots of Cochliomyia spp and Chrysomya spp), sheep nasal bots (Oestrus ovis), and sheep keds (Melophagus ovinus). The molecular mode of action closantel is not completely elucidated, but closantel decouples the mitochondrial oxidative phosphorylation, which leads to the inhibition of ATP synthesis, this seems to occur through suppression of the activity of succinate dehydrogenase and fumarate reductase, two enzymes involved in this process. Finally this all cause the death of the parasite. Recently it has been discovered that closantel also inhibits chitinase in Onchocerca volvulus, a filarial nematode causing river blindness in humans. Chitinase is an enzyme involved in larval molting. Its inhibition interrupts their development to adult worms. This drug possesses some side effects: hyper acute anaphylactic reactions in cattle; hypersensitivity reactions; overdoses can cause reduced visibility or blindness, anorexia, lack of coordination and general weakness.