Nitazoxanide, a nitrothiazolide antiparasitic drug, is an anti-Helicobacter pylori agent with anti-vacuolating toxin activity.

Nitazoxanide (NTZ), a synthesized drug of the nitrothiazolide class, was initially developed as an antiparasitic compound. This compound has recently been shown to have antibacterial activities against some bacterial pathogens. In the present study, NTZ and its main metabolite tizoxanide (TIZ) were found to have strong minimum inhibitory concentrations (MICs) against both metronidazole (MTZ)-resistant strains and sensitive clinical isolates of Helicobacter pylori. The MIC90 of both NTZ and TIZ against 37 clinical isolates was 8 microg/ml. Vacuolating toxin activity of H. pylori assayed by HeLa cell vacuole formation was inhibited by NTZ at a sub-MIC. In contrast, urease production by H. pylori was not specifically affected by the sub-MIC of NTZ. An acidic pH (pH 5.0) medium reduced the antimicrobial activity of the drug in terms of growth inhibition due to the low growth rate of the bacteria, but killing activity of NTZ against the bacteria was still observed. Thus, it was apparent that both NTZ and TIZ are highly effective against H. pylori, even when the bacteria are resistant to MTZ.