Enhanced antinociceptive efficacy of epidural compared with i.v. methadone in a rat model of thermal nociception

Epidural administration of methadone in rats resulted in systemic exposure similar to that after i.v. administration, but improved thermal antinociceptive efficacy, and reduced supraspinal undesired effects. The findings suggest the presence of local effect at the spinal cord level, in addition to the systemic effect produced by epidural methadone.