Systemic administration of magnesium sulfate enhances lidocaine-induced sciatic nerve block and exerts analgesic effects in postsurgical pain in rats

Purpose: Magnesium plays a role in various physiological processes and has been used for treatment and prevention of diseases affecting different organ systems. Magnesium sulfate, has been proposed as a potential adjuvant for anesthesia, yet its efficacy remains controversial due to limited and conflicted previous findings. The present study explored the analgesic effects of different routines of magnesium sulfate administration under three common perioperative situations in rats. Methods: Three experimental settings were evaluated: (1) perineural co-administration of magnesium sulfate with lidocaine, (2) systemic intraperitoneally magnesium sulfate pre-administration before lidocaine nerve block, and (3) systemic magnesium sulfate given before or after plantar incision surgery. Sensory/motor blockade duration and mechanical pain thresholds were assessed. Results: Magnesium sulfate attenuated lidocaine induced sciatic nerve blockade when applied as an adjuvant to lidocaine, whereas enhanced lidocaine induced blocking effects when magnesium sulfate was injected intraperitoneally. Pre- or post-operative intraperitoneal injection of magnesium sulfate attenuated postsurgical pain in a plantar incision model in rats. Conclusion: Magnesium sulfate exhibits route-dependent effects: while it attenuates lidocaine-induced nerve blockade when administered locally, it enhances blockade duration and provides significant analgesia when given systemically. These findings provide evidence for the potential of magnesium sulfate as an adjuvant for optimizing anesthesia and pain management protocols.