Several adjuvants such as fentanyl, alpha-2 adrenergic agonists (clonidine or dexmedetomidine), tramadol, and magnesium have been used to extend the duration of peripheral nerve blocks. 5-7 Magnesium has antinociceptive effects in animal and human models, principally related to blocking the N-methyl-D-aspartate (NMDA) receptors and regulation of calcium influx into cells. Calcium influx leads to a sequence of central sensitization such as windup phenomenon and long term potentiation which are crucial mechanisms that determine the duration and intensity of post-operative pain. Magnesium prevents central sensitization triggered by peripheral nociceptive stimulation in response to painful stimuli.