Lack of pre-emptive analgesic effects of local anaesthetics on neuropathic pain

We investigated the significance of pre-emptive analgesia using a well-known model of neuropathic pain in rats. Lignocaine, bupivacaine or saline was applied locally to the left L5-L6 spinal nerve before or 4 days after nerve injury. Mechanical allodynia was then evaluated before and after injury. Pre- and post-injury treatment with local anaesthetics both resulted in a two- to threefold increase in the pain threshold, as manifested by a significant increase in von Frey measurements. However, this effect lasted only 24 h. Our study in rats questions the beneficial effect of a single dose of local anaesthetic as pre-emptive analgesia.