Nitazoxanide is a nitrothiazolyl-salicylamide derivative and belongs to the thiazolide class. The chemical structure is 2-acetyloxy-N-(5-nitro-2-thiazolyl) benzamide, and the molecular formula is C12H9N3O5S (Figure 186.1). The molecular weight is 307.28 g/mol. The benzamide structure resembles niclosamide, a drug used to treat tapeworm infections, whereas the nitrothiazolyl ring shares homology with the nitroimidazole drugs metronidazole and tinidazole (see Chapter 99, Metronidazole, and Chapter 100, Tinidazole). Nitazoxanide was first described in 1975 by Jean Francois Rossignol at the Pasteur Institute in Paris, France, and originally was developed as a veterinary anthelmintic. Initial human studies in the 1980s revealed its efficacy in treating human tapeworm infections (Rossignol and Maisonneuve, 1984). Subsequent in vitro and clinical studies have demonstrated an unusually broad antimicrobial spectrum that transcends taxonomic classes, with activity against protozoan parasites, helminths, anaerobic bacteria, mycobacteria, and viruses. A series of controlled trials conducted by Romark Laboratories established the efficacy of nitazoxanide for the treatment of giardiasis and cryptosporidiosis in immunocompetent patients, leading to approval in the United States for the treatment of Cryptosporidium species and also Giardia infections. The drug is also approved in many Latin American and Asian countries for the treatment of a range of intestinal helminths.