Broad-spectrum antiparasitics, analogous to broad-spectrum antibiotics for bacteria, are antiparasitic drugs with efficacy in treating a wide range of parasitic infections caused by parasites from different classes.
Early antiparasitics were ineffective, frequently toxic to patients, and difficult to administer due to the difficulty in distinguishing between the host and the parasite.
Between 1975 and 1999 only 13 of 1,300 new drugs were antiparasitics, which raised concerns that insufficient incentives existed to drive development of new treatments for diseases that disproportionately target low-income countries. This led to new public sector and public-private partnerships (PPPs), including investment by the Bill and Melinda Gates Foundation. Between 2000 and 2005, twenty new antiparasitic agents were developed or in development. In 2005, a new antimalarial cost approximately $300 million to develop with a 50% failure rate.
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^Di Santo N, Ehrisman J (2013). "Research perspective: potential role of nitazoxanide in ovarian cancer treatment. Old drug, new purpose?". Cancers (Basel)5 (3): 1163–1176. doi:10.3390/cancers5031163. PMC3795384. PMID24202339. Nitazoxanide [NTZ: 2-acetyloxy-N-(5-nitro-2-thiazolyl)benzamide] is a thiazolide antiparasitic agent with excellent activity against a wide variety of protozoa and helminths. ... Nitazoxanide (NTZ) is a main compound of a class of broad-spectrum anti-parasitic compounds named thiazolides. It is composed of a nitrothiazole-ring and a salicylic acid moiety which are linked together by an amide bond ... NTZ is generally well tolerated, and no significant adverse events have been noted in human trials . ... In vitro, NTZ and tizoxanide function against a wide range of organisms, including the protozoal species Blastocystis hominis, C. parvum, Entamoeba histolytica, G. lamblia and Trichomonas vaginalis 
^Hemphill A, Mueller J, Esposito M (2006). "Nitazoxanide, a broad-spectrum thiazolide anti-infective agent for the treatment of gastrointestinal infections". Expert Opin Pharmacother7 (7): 953–64. doi:10.1517/146565126.96.36.1993. PMID16634717.