Spinal antinociception: clinical aspects.

Recent research has demonstrated the increasing importance of the spinal cord in processing and modulating nociceptive input. Different groups of drugs, each acting by a unique mechanism, have been shown to block nociceptive afferent transmission. None of the currently available spinally administered local anesthetics, opioids or non-opioids produce analgesia without side effects. Non-opioids such as alpha-2-adrenergic agonists may be more suited as adjuvants rather than sole analgesic agents and their main role lies in reducing the dose requirements of other analgesics. Spinal somatostatin and ketamine may have neurotoxic potential. The role of these drugs and of midazolam in pain management appears to be limited. Preliminary results suggest that the neuropeptide octreotide has potent analgesic effects. 'Balanced spinal analgesia' using a combination of low doses of drugs, with separate but synergistic mechanisms of analgesia, may produce the best results. The optimal drug combinations and dosages remain to be determined. It is essential that animal neurotoxicity studies followed by controlled clinical trials are performed before widespread spinal administration of new drugs.