[The effects of epinephrine added to epidural morphine]

The authors studied the influence of epinephrine added to epidural morphine on morphine pharmacokinetics. Epidural morphine 3mg in 10ml of saline solution was administered from the Th11-12 interspace to 14 patients undergoing right thoracotomy. In addition, epinephrine 50micrograms was added to the epidural solution in 8 patients selected randomly. Morphine concentrations in the azygos vein and radial artery samples were measured. Compared with the plain morphine group, addition of epinephrine significantly decreased morphine concentrations in the azygos vein only at 5 and 10min after administration. At 15 and 30min after administration, the azygos vein morphine concentrations in the epinephrine group were at the same level as in the plain morphine group. The admixture of epinephrine with epidural morphine increased the individual variation in the half life of morphine concentrations in the azygos vein. All these results suggest that addition of epinephrine does not play a particularly important role in causing prolonged and profound analgesia after epidural morphine.