Zerofen 22% is a broad-spectrum anthelmintic for the treatment of horses and other equines infected with benzimidazole susceptible immature and mature stages of nematodes of the gastro-intestinal tract including large redworms (Strongylus vulgaris, Strongylus edentatus) and migrating large redworms, small redworms and encysted mucosal larvae, Ascarids, Oxyuris and Strongyloides species. Zerofen also has an ovicidal effect on nematode eggs.