After passive diffusion into susceptible organisms, tinidazole's nitro group is reduced by low-redox-potential electron transport proteins such as ferredoxin and flavoprotein nitroreductases. This reduction generates short-lived nitro radical anions that covalently bind DNA, produce strand breaks, and inhibit nucleic acid synthesis. Because activation requires anaerobic or microaerophilic conditions, the drug spares aerobic host tissues while producing potent concentration-dependent killing against Giardia, Entamoeba, Trichomonas, and Bacteroides species.