Magnesium sulfate for postoperative analgesia after surgery under spinal anesthesia.

Background: Magnesium has been proven to have antinociceptive effects in animal and human models of pain. Its effect is primarily based on the regulation of calcium influx into the cell, which is natural physiological calcium antagonism and N-methyl-d-aspartate (NMDA) receptor antagonism.

Methods: One hundred and eight patients undergoing surgery with spinal anesthesia received either 250 mg of intravenous magnesium sulfate followed by an infusion of 500 mg magnesium sulfate (25 mg/mL) at the rate of 20 mL/hour; or the same volume of normal saline (control group) as bolus and infusion.