Role of epidural and intrathecal narcotics and peptides in the management of cancer pain.

The spinal administration of opioids may provide analgesia of long duration to patients with bilateral or midline lower abdominal or pelvic cancer pain. However, cross-tolerance to orally and parenterally administered narcotics and the rapid development of tolerance to spinal narcotics have limited their usefulness. Opioids have extensive distribution in the CSF and plasma when administered into the epidural or intrathecal space, and delivery of drug to brain stem sites may account for many of the toxic and therapeutic effects of spinal opioids. Further clinical and pharmacokinetic studies are required to provide the information regarding: the optimal opioids for use as spinal analgesics; equieffective dose ratios of spinal opioids in comparison to parenteral or oral opioids; strategies useful to forestall the development of tolerance of spinally administered opioids; the analgesic efficacy of this therapy in opioid-tolerant patients; and the role of spinally administered nonopioid analgesics in the management of cancer pain in the tolerant patient. These questions will need resolution before this therapy can be recommended for routine use in the management of cancer pain.