Magnesium is implicated in the activation of NMDA receptors by amino-excitatory acids in the
central nervous system [1]. Magnesium deficiency is associated to an increased activation of
these receptors, and to an increased sensitivity to pain in animals. Spinal cord is the site
of sensitization of pain, mainly mediated by the NMDA receptors, and intrathecal magnesium
may have anti-hyperalgesic effect when administered intrathecally [2]. As intrathecal
magnesium has already been used in humans for treatment of eclampsia, we stated that it could
also improve postoperative analgesia and reduce the need for auto-administered morphine if
given (50 mg of magnesium sulfate) with the intrathecal anesthetic drugs (bupivacaine and
sufentanil) injected for orthopedic surgery.