The efficacy of intrathecal morphine and clonidine in the treatment of pain after spinal cord injury

We performed a double-blinded, randomized, controlled trial in 15 patients to determine the efficacy of intrathecal morphine or clonidine, alone or co mbined, in the treatment of neuropathic pain after spinal cord injury. The combination of morphine and clonidine produced significantly more pain reli ef than placebo 4 h after administration; either morphine or clonidine alon e did not produce as much pain relief. In addition, lumbar and cervical cer ebrospinal fluid (CSF) concentrations, sampled at these levels at different times after administration were examined for a relationship between pain r elief and CSF drug concentration. Lumbar CSF drug concentrations were initi ally several orders of magnitude larger than those in cervical CSF. After 1 -2 h, the concentrations of morphine in cervical CSF markedly exceeded thos e of clonidine. The concentration of morphine in the cervical CSF and the d egree of pain relief correlated significantly. We conclude that intrathecal administration of a mixture of clonidine and morphine is more effective th an either drug administered alone and is related to the CSF-borne drug conc entration above the level of spinal cord injury. If there is pathology that may restrict CSF flow, consideration should be given to intrathecal admini stration above the level of spinal cord damage to provide an adequate drug concentration in this region.