Nitazoxanide (Alinia, Romark Laboratories) was synthesized based on the structure of niclosamide. In vitro studies have demonstrated activity against a broad range of parasites as well as some bacteria. Three controlled trials demonstrated efficacy in cryptosporidiosis, however, the efficacy in advanced AIDS patients (CD4 cell counts = 50) at approved doses was limited. Trials have also demonstrated efficacy comparable to metronidazole (Flagyl, GD Searle and Co.) in giardiasis with fewer side effects. Nitazoxanide is also effective versus intestinal helminths and tapeworms as well as in chronic fascioliasis. Side effects in clinical trials have been similar to placebo. Nitazoxanide is the first agent proven to be effective in cryptosporidiosis. It has also proven efficacy in giardiasis. Nitazoxanide is efficacious again intestinal helminths. Additional indications may be developed in the future.