Metronidazole does not show direct antioxidant activity in global systems.

Metronidazole has been widely used topically and systemically for more than 50 years but data on its antioxidant properties are still incomplete, unclear and contradictory. Its antioxidant properties are primarily hypothesized based on results, therefore, studies have been performed to determine whether metronidazole has antioxidant activity . We used so-called global spectrophotometric and luminometric methods. Fe/Fe-reducing ability, hydrogen donor activity, hydroxyl radical scavenging property and lipid peroxidation inhibitory activity were investigated. Under the condition used, metronidazole has negligible iron-reducing ability and hydrogen donor activity. The hydroxyl radical scavenging capacity cannot be demonstrated. It acts as a pro-oxidant in the HO/OH-microperoxidase-luminol system, but it can inhibit the induced lipid peroxidation. According to our results, metronidazole has not shown antioxidant activity but can affect redox homeostasis by a ROS-independent mechanism due to its non-direct antioxidant properties.