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Reactive oxygen species (ROS) generated from neutrophils accumulated in various major organs are thought to play a pivotal role in the pathogenesis of host auto-injury. Lidocaine has been shown to reduce the injury. We investigated the effect of local anaesthetics (lidocaine, mepivacaine and bupivacaine) on ROS production by neutrophils using an in vitro system.We measured the production of superoxide (ferricytochrome c method), hydrogen peroxide (H2O2: scopoletin fluorescence technique), and hydroxyl radical (OH: ethylene gas method) by neutrophils isolated from human adult volunteers in the absence and presence of lidocaine (2-200 µg/mL), mepivacaine (3-300 µg/mL), and bupivacaine (3-300 µg/mL). We also measured the ROS generation in a cell-free (xanthinexanthine oxidase) system.Lidocaine and mepivacaine at higher levels significantly decreased the production of ROS by neutrophils. However, these local anaesthetics at clinically relevant blood concentrations had no effect on the levels of ROS. Furthermore, lidocaine and mepivacaine failed to reduce ROS generated by the cell-free system. Bupivacaine did not decrease ROS generation by either generating system.In conclusion, in the present in vitro system, only concentrations of lidocaine and mepivacaine 100-fold higher than clinically feasible ones reduced ROS production by human neutrophils. However, the local anaesthetics at clinically relevant blood concentrations had no suppressive effect. Further studies using in vivo systems are required to elucidate the inhibitory effects of local anaesthetics on ROS generation in clinical settings.